Did they adopt different strategies?

Definitely, after suffering catastrophic losses early in the Campaign, Bomber Command went to night time bombing to minimise losses to ~5% per night (still wastage of a couple of hundred men). The USAAF stayed with daylight bombing despite suffering massive losses early on too, but the appearance of fighters with the range to escort bombers dropped the loss rate down to a more acceptable level. (I am not sure what acceptable was in this case, I heard it was 5%, but I am not certain on that.)

Were they ever at odds with each other about what targets to attack, how and what with?

There was some debate between Sir Arthur Harris (CinC Bomber Command), Eisenhower and the commanders of the 8th of what was to be targeted and other commanders further up the chain. (Harris would often deride targets he was instructed to attack by Sir Charles Portal, Marshall of the RAF as being Panacea targets in favour of attacking cities for their industrial, transport and economic targets. Targeting priorities would regularly change, which may have not helped the war effort from the perspective of the input from the bombers.

How true is it that the 8th Air Force operated during the day whilst Bomber Command operated at night?

It is very true. The RAF switched to night bombing during 1940 to cut down losses, only returning to daylight bombing around D-Day, when they would attack high-priority targets during the day. (V1/V2 sites, targets in France etc.) The USAAF stuck with daylight bombing, despite almost being destroyed as a bombing force during the first few months of their campaign.

If approaches were different, was one notably more accurate than the other and what methods were adopted to improve accuracy?

Yes, the USAAF attempted to be more accurate with the use of formation flying and the Norden Bomb sight. By the end of the war however, they were using "carper bombing" like the RAF before them and the Luftwaffe before that.

The RAF did a survey in late 1941 (if I recall, I will have to check) in which they ascertained that only about 25% of bombers were actually attacking their targets and bomb creep was an issue. To get around this, the RAF instigated the Pathfinder Force under Don Bennet who set up the pathfinder fore (PFF). They would fly ahead of the main force (usually in Lancasters or Halifaxes) and drop flares along the route to guide the bombers as well as marking targets using a number of techniques such as the Paramatta technique, which was ground marking with flares, or air marking using flares in parachutes (Warangui or something, I need to check the name). They used electronic techniques such as GEE, OBOE and H2S to locate targets themselves.

Eventually, the Master Bomber technique was developed which would lead to greater accuracy amongst bomber crews, as they would be instructed on what markers/fires to attack. This was a very useful technique, which was proven by a precision attack, at night, on the Michelin Tyre Factory.

How effectively were joint operations, such as OVERLORD, co-ordinated?

Despite grumbling from Sir Arthur Harris, RAF Bomber command did switch to attacking communications and transport hubs in preparation for D-Day and continued to attack these targets until the end of the war. Cooperation between the air forces and the planners of D Day could definitely have been better, but it was done.

Was targetting civilians a deliberate aim, or simply an unfortunate by product?

This is a very contentious topic for a number of reasons. Some will say that civilians were definitely targeted and point you towards Hamburg and Dresden to champion their cause but the reality was much more complicated than that, as the Hamburg firestorm was a result of the unique construction features of the city and Dresden was the result of a miscommunication of the raid results to Washington and some very good propaganda by Goebbels which resulted in an estimation of casualties of 600 000, rather than the initial SS estimate of 50-60 000.

Harris also managed to shoot himself in the foot with comments in his autobiography about deciding to attack cities to take some of the pressure off of his crews.

However, civilian casualties were an unfortunate inevitable side effect of the targets attacked (industrial areas/marshalling yards etc in highly populated areas) and the instructions given to Harris when he started his campaign to destroy the German war economy.

Obviously, I have oversimplified some of the topics discussed, but it should serve as a starting point. I will add a few books that might help you with learning more about the RAF side of the story tonight when I get home.

It is true that 8th Air Force operated during the day and Bomber Command operated at night. It is also true that at least for Bomber Command, civilians were directly targeted, night bombing simply wasn't accurate enough to target individual factories or other point targets. For that matter, the 8th Air Force's Norden bombsight wasn't anywhere near as accurate as advertised, many of their bombs failed to hit their targets, but the entire point of daytime bombing was that it was more accurate than nighttime bombing.

The reasons for Bomber Command operating at night and the 8th operating during the daytime come down to bomber protection. The British simply couldn't keep up with the attrition to their bomber fleet during the daylight, and moved bombing to night when air defenses of the time were less effective. The 8th on the other hand, with its B-17s and B-24s, felt that their bomber's had enough onboard protection to defend themselves. This was proven to be overly optimistic during missions like Regensburg and Schweinfurt.

As for accuracy, daytime bombing was much more accurate, though both sides attempted to improve accuracy. The British did this by sending in faster, more easily defended, and more accurate Mosquito light bombers to act as "pathfinders," illuminating targets for the larger Lancasters, Halifaxes, and Stirlings. It should also be mentioned that even the US daytime bombing, while more accurate than that of the British, was still woefully inaccurate, with only 7% of all bombs dropped by the 8th Air Force landing within 1,000 feet of their aimpoint.

Targeting civilians was very much a direct aim from the beginning with British nighttime area bombing, and in large scale attacks on cities like Hamburg and Dresden the United States picked up the tactic as well.

Targeting priorities were altered in order to support Operation Overlord.