I'll just copy & paste a comment I made a few weeks ago (with a few edits) on this very topic! I hope you don't mind.

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I have the daily schedule of one Captain Geoffrey Bowen with the 2nd Battalion Lancashire Fusiliers on September 3rd, 1917. I'll be giving some context in brackets throughout for reading sake:

8.pm. Started [wake up]
9.30 p.m. Arrived. [at trench]
11 p.m. Company arrived.
11 p.m.-3 a.m. Round the line [ie: checking on men, checking positions, maintaining quality control across the line]
3.15 a.m.-4.15 a.m. Sleep
4.15 a.m.-6.am. Stand to. [Night watch, essentially]
6 a.m.-6.30 Reports [from lower level officers]
6.30a.m.-9. Sleep
9 a.m.-9.30 Breakfast: bacon, eggs, tinned sausage
9.30 a.m.-10.10 Round the line
10.10 a.m.-12. Reports, etc.
12.30 p.m. Lunch: Steak, potatoes, beans, sweet omelette
1.45 p.m.-2.15. Daylight patrol.
2.15 p.m-2.30. Sleep.
2.30 p.m.-3.40. Gup [gossip, idle chat] with the C.O. 
4 p.m. Tea, bread, jam.
4.30 p.m.-4.35. Sleep.
4.35 p.m.-5.10. Entertain 'Bowes' 
5.10 p.m.-5.15. Sleep.
5.15 p.m.-5.25. Trench Mortar Officer reports.
5.25 p.m.-6.15. Sleep
6.15 p.m.-6.35. Entertain Brain and Padre [Chaplains, implied work on mental and religious health]
6.35 p.m.-7.30. Sleep.
7.30 p.m.-8. Round the line
8 p.m.-8.15. Dinner: steak, potatoes, tinned fruit and custard.
8.15 p.m.-9. Round the line
11.30 p.m.-12.30 a.m. Sleep.
12.30-2.30 a.m. Intensive sniping [under fire]
2.30-5 a.m. Sleep.

It's not nearly as dramatic as you may think. The unfortunate truth for Hollywood is that most of WWI was sitting around improving defenses and doing basically nothing. The conditions were horrific the entire time for most parts but you were not constantly getting out of trenches and charging enemies most of the time. One of the biggest jobs of men on the front is to constantly check, repair and lay down barbed wire outside of their trenches. This was generally done at night for obvious reasons and generally required hundreds of men to cover the workers doing this. At first they had to use mallets and even if they tried to muffle the sound by putting sandbags between the mallet and the stake to hold the barbed wire down, it was still noisy business. This brought the attention of many snipers. Eventually a corkscrew type of device would be universalized which would allow men to 'screw' the stake into the ground silently.

However the amount of fighting and what fighting you got depended on your sector. There were generally two types, quiet and loud sectors. Loud sectors were ones where the trenches were extremely close to the Germans -- at times less than 25 yards away but usually no further than 100-200 yards away. You are in constant threat of rifle fire but not so much artillery lest each side hits their own men. So your entire existence is painted by avoiding snipers, being under sniper fire, and having bursts of machine gun fired in your general direction in your daily life. The quiet sectors were generally very different. You could easily be 600-800 yards away from the other trench and both sides adopted a 'live and let live' philosophy and your greatest threat would be random artillery barrages from miles away. Capt. Dugdale described the experience:

Time passed very peacefully, as the Germans were very quiet. My battalion snipers had the time of their lives; never before had they been given such targets. We literally kept a game book of hits for hte first three days; after that the Germans did not show themselves so much; also they started to retaliate.

Wiring was carried out nearly every night, but not in the style we were accustomed to in the days of the Somme. Our men did not creep through the wire carrying coils of wire, stakes, etc.; instead, a general service wagon was driven into No Man's Land with the materials on board, which were dumped out when required. At first we expected bursts of machine gun fire every minute, but nothing happened. It must have become a well-established custom, as the enemy did the same thing themselves; we did not interfere.

Nonetheless in the general, the Germans were very keen on disrupting workers parties; particularly with machine guns and offensive patrols. The need for quiet was imperative but not always followed by the more reckless green horns. One account by Henry Gregory describes a particularly loud worker party shouting orders and joking with each other while his company was covering their duties. After about 30 minutes of it the Germans (who were previously pretty quiet) got fed up and unleashed a massive mortar barrage and machine gun attack on the position, killing dozens of men who had no reason to be dying that night.

Conditions in the trenches were universally pretty horrible; that is one universal thing that can be applied. Many trenches had water up the knees of men and you would have to wade around in this grungy, dirty mud water all day and everything you had would be almost constantly wet. When digging new trenches it was not uncommon to get a sudden and sharp scent of a dead body lying there for weeks or months as you pierced his flesh in the dirt, especially in when repairing trenches taken over from the enemy after large artillery barrages.

Everything, once you got up to the front, had to be carried by hand for obvious reasons. Usually in the dark. In knee to waist high water. While being shot at by snipers consistently. You can imagine the frustration and how it could wear on a man. Thankfully soldiers would be cycled out weekly or monthly (depending on the sector and how much combat is being seen) so you would only deal with these extra harsh conditions on the front for a short burst of time before getting some rest / being assigned to a trench further back.

That's really what made the war so horrible though for men on the front. You didn't attack all that much but your life was still a miserable hellhole. You sat in a crappy trench while being shot on constantly by snipers or being bombarded constantly by artillery depending on where you were -- if you were in a perfect spot both at once! You were constantly slightly hungry because of poor rations and if someone slipped and dropped a box of steak in water you would just have to go hungry; an experience that happened enough for men to justify writing about it as a part of their experience.

However, for all that, the actual combat was pretty minimal and dare I say routine, especially for quiet sectors. Your duties if you were a rifleman were essentially forward patrols from time to time and covering worker parties (usually the two duties were combined) which was a dangerous job but not really an all out attack and otherwise maintaining the trench system through constant labor. If you were a machine gunner or a sniper your life was essentially to sit in one spot for hours and harass the enemy and discourage them from performing their own maintenance or making them do it under great duress. And if you were an officer your job was basically to walk around and make sure everyone was doing their job correctly.

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Notes:

Holmes, Richard, "Tommy: The British Soldier on the Western Front "

Simpson, Andy "Hot Blood & Cold Steel: Life and Death in the Trenches of the First World War"