The idea of using aircraft for military operations was not new. Balloons were employed for observing / reconnaissance as early as 1795, in the battle of Fleurus in 1794 (1)

(note the difference between Aircraft, which is anything that flies, and airplane: the thing with wings and an engine in this case)

so initially when the powered airplane came along it was used in addition to the balloons for exactly the same purposes, as it was logically far more maneuverable, and thus less vulnerable than a balloon.

Though the first recorded instance of an aircraft used for bombing (AFAIK) was in Libya by the Italians 1911-1912 (2)

I will take a further look at the WWI tactics for aircraft through Germany, as this is an area I have studied and arguably they were ahead of the allies for the duration of WWI with regards to the use of airpower.

The germans had identified several roles for Aircraft just prior to WWI (2):

-Strategic Reconnaissance

-Tactical Reconnaissance

-Artillery Reconnaissance

-Reconnaissance for Cavalry Divisions

-Fighting enemy aircraft

-Fighting Ground Troops

-Destroying Enemy Installations

-Liaison (message Carrying)

-Troop Transport

As you can see most roles are dedicated to reconnaissance. This is also the role in which they proved to be a valuable instrument in the first stages of the war: The encirclement and destruction of the Russian second army by the German Eight army at the battle of Tannenberg would not have been possible without the reconnaissance intel gathered by aircraft (3)

The Germans also planned strategic bombing missions beginning as early as 1915, through airships, even though they had a short-lived psychological impact on the Population of London against which they had been deployed it was considered a failure because of the losses the Germans suffered. (4)

The next major step was the development of the dedicated fighter airplane on both sides. It was understood that in order for aircraft to carry out what was considered their primary role: Reconnaissance and now bombing, air superiority had to be won. Thus necessitating a airplane dedicated to down other aircraft. During 1915/1916 aircraft to suit this purpose were developed. The Germans used them during the Battle of Verdun to guard their own Artillery Reconnaissance aircraft, and to down enemy reconnaissance flights.(4)

During the 1916-17 period The Germans realized that a purely Defensive use of aircraft would not lead to decisive results, they needed to be used offensively as well. (5)

The air campaign in Flanders during 1917 saw the first German unit dedicated to close air support (CAS), and in the same year the first German manual for ground attack squadrons was issued by the high command. it also saw the first anti-airfield campaigns as German heavy bombers carried out raids against the French and British airfields. (6)

In the Period May 1917 - May 1918 the Germans rolled out a strategic bombing campaign using airplanes against London, but this was eventually abandoned as losses outweighed the benefits of this operation. Mostly due to the technical limitations of the airplanes of the era. (7)

So basically the strategies used by the airfares were eventually different for each specific roles.but they all relied on one key concept, which the Germans realized quite early on: Air Superiority through dedicated fighter aircraft. In general there was a notion of strategy and different roles at the outbreak of WWI, but one could say it was mainly an era of trial and error for air power: starting out with reconnaissance as the main role, then developing fighter aircraft to protect these reconnaissance machines from getting shot down, and CAS aircraft / bombers and strategies to further gain air superiority, by attacking enemy airfields for instance.

In how far the strategies for the ground forces differed with the rise of the Airplane I don't know. I doubt much changed, as said earlier the use of ballons for observation was in use some 100 years already. The only difference I can think of is of top of my head is the introduction of Anti-Aircraft guns, though one could argue that these were already being used against ballons / airships. Close Air support was in its infants shoes during WWI, and in general is a more mobile replacement for Artillery allowing forces more mobility, which in WOI with the trench warfare doesn't have that much of an impact.

Sources

(1)https://archive.org/stream/worldsgreatestwa01thomuoft#page/242/mode/2up

(2) James S. Corum, The Luftwaffe: Creating the Operational Air War, 1918-1940 (Lawrence, KA: University Press of Kansas, 1997), p.22

(3) Corum, The Luftwaffe, p.23

(4) Corum, The Luftwaffe P.24-25

(5) Corum, The Luftwaffe P.28

(6) Corum, The Luftwaffe, P.29-34

(7) Corum, The Luftwaffe, p.34-37

In 1914 aircraft were used by all sides for observation, and for most air forces this was their only role. It is worth remembering that this was the very infancy of flight, merely to go up in an aeroplane was dangerous. Planes were extremely fragile and just to maneuver one was a tricky task, as they could fall apart under the stresses of just turning or diving. Payloads were very, very limited, speeds very low, climb rates the same.

Nevetheless, enterprising airmen were soon shooting at each other with any weapon they could carry aloft, and although the risks were at first small, squadrons began to include aircraft to protect their observation planes. Men with unusual skill at flying and shooting could bring down an enemy with a rifle or shotgun, or even a machine gun in the few planes that could carry one and allow it to fire (usually by being 'pusher' aircraft with the propeller at the back).

In 1915 the French pilot Roland Garros used an aircraft that could fire its gun through the propeller to shoot down several German aircraft in a short period, before he was himself shot down and the Germans examined his plane. They realised that they needed to produce something similar, and Anthony Fokker delivered in a short time with the Fokker Monoplane. It is about fair to say that 1915 saw the dawn of meaningful air fighting, and the Fokkers were highly successful. The French replied soon after with the Nieuport Bebe, the British with the DH-2 among others. Although neither of these could fire their machine gun through the propeller, they were intrinsically better aircraft than the Fokker and air combat became a regular occurrence, albeit on a very small scale relative to later. Observation and scouting remained the primary goals of all air forces, and this became more important as 1916 wore on and all sides looked to mass artillery bombardment as a way to break the trench deadlock. Over the Somme, a large British effort and the slight superiority of the DH-2 and Vickers 'Gunbus', and later the Sopwith Pup, saw the Fokkers totally outclassed and driven from the skies- of course along with the German observation ('C' type) planes.

Responding to this, the German pilot Oswald Boelcke formed a new doctrine of fighting: he would group the fighter planes together, rather than attacking a few to each squadron of observer planes. Tactics would be publicised to pilots, understood, and the emphasis was on a team effort. Rather than a free-for-all, he would allow the Allied planes to come to him, or mass against them to achieve local superiority of numbers.

Just as he was working out his tactics and forming the first fighter squadrons, the jastas, Germany introduced their answer to the Nieuport and Sopwith, the Albatros DI. With two machine guns firing forward and decent handling and reliability, this combination of aircraft and tactics changed air warfare over the Western Front in early 1917.

Interestingly, the French had arrived at a similar conclusion with regard to organisation at a similar time, grouping their talented fighter pilots into squadrons like N-3, 'The Storks', so they could achieve concentration. The British were soon doing the same, forming the elite 56 Squadron, but not before they suffered massive losses during 'Bloody April' 1917.

The changes described in the last paragraph led to air warfare emerging into a 'modern' form. Previously, the aces were exceptional 'lone wolves', who often fought on their own. Planes were still inherently fragile, tactics a matter of trial and error, air combat an uncoordinated melee. 1917 changed all that.

Aircraft underwent a real change in 1917, as the first generation of World War I aircraft were supplanted by the fighters that were to see the sides through to the end of the war, the SPAD, SE5a, Camel as well as some other, better two-seaters. Germany had to soldier on with the Albatros until 1918. It really needed replacing six months earlier, but the performance differential was so small that it was still shooting down Allied aircraft until the end of the war.

Observation aircraft had little in the way of tactics that could help them. The British in particular emphasised that they should always be carrying out this work, and their pathetic observation planes had to fly straight and level to do their work. They had little chance to defend themselves if attacked, and 'Bloody April' saw swathes cut through the ranks of BE2s, RE8s and Sopwith 1 1/2 Strutters. The Royal Aircraft Factory, the government-run facility that designed most, but not all, British aircraft, stuck to a doctrine that observation planes should be very stable and able to fly 'hands off', the very opposite of what was needed for survival in air combat.

Aces High Alan Clark Bloody April Peter Hart

Wow, very detailed response. Thank you very much