Downloaded Verdun yesterday. I've only played a couple of games but so far I have zero idea what going on or what I'm supposed to do. All I know is that I die a lot.
Ok, so the first thing you need to know is this:
If you can see the enemy, the enemy can see you. Especially observant snipers.
You dont want to poke your head out in an area for too long on defense because a good offense team will generally have a sniper that hangs back and tries to pick off MGs and other targets of oppritunity. Barring that, a good NCO will be able to call devestating barrages on you if you are too static and visible.
On offense, the best way to advance is patiently. Prone is your friend; the way the sprint button works is that it leaves you in the position you were in when youre done sprinting. So, what you want to do estensially is sprint into cover to cover, lying prone in the various craters in between. Its not the quickest way to the enemy trench, but its the hardest way for the enemy to gun you down. Speaking of, if an enemy MG is trying to pin you, just hide behind cover and dont be a hero. If you dont try to leave, its just wasting ammo and time which it could be using defending somewhere else.
If you play MG yourself, one trick I dont see enough is deploying you MG in no man's land and firing a few bursts into the trench while your friends advance. Its very risky; you broadcast yourself quite clear where you are, but it draws out where the enemy is, actually making it easier for you or your team to pick them out. And if you guess correctly and you fire where the enemy physically is, they tend to panic and just stay down, giving cover for your advancing squad.
As for squads and roles, I think the basic squads (polius, tommies, doughboys, and landsers) are the best for new people due to their tatical flexibility. They do have a defense orientation, due to having both a sniper and an MG, but theyre very staight foward in what they do. They have the most intuitive spawning system (spawn on the NCO if they are alive, randomly in your trench otherwise) and barrage (just a simple mortar barrage, which gets more powerful if you level up your squad), plus they dont have much in the way of gimmicks that you have to account for while playing as them.
Recon is the most useful squad type imo, but theyre also the least fun to play, so I understand if people dont like picking them. They dont get a barrage, but the recon plane they get instead is super useful to show everyone on your team where the enemy is currently located. Recon also has the mechanically most useful spawning system (spawn on the furthest ahead player; which is the only spawning system not reliant on the NCO to function. Recon gives a lot of offensive pressure because you need to kill every recon player in that squad at once to prevent foward spawns) Plus, while they dont get MGs or other heavy weapons, their carbines are really amazingly strong (The Kar98AZ that the German recon uses is honestly the best rifle in the game hands down).
With sentries, you trade a lot of your offensive potential for amazing durability. Their barrage (a single, but supercharged, artillery shell) is pretty niche due to having a long time between call in and when it actually fires, and you have the worst spawn system of them all (spawn on any player... In your own territory only. Its estensially only is worth a damn when youre being routed in your trench and a new wave spawns, which means your squad will regroup quicker than others). However, sentry squads have increased durability compared to other squads, which can meanthe difference of surviving that fire fight or not. They also get better MGs, especially the German sentries, and really in general get better weapons for trench warfare than other squad types.
Engineers and Assault squads are pretty similar; they are your main form of offensive pressure when you are the ones assaulting the trench. The differences between the two are minute but noticable. Assaults get a special spawn sytstem where they spawn on the attack order if a squad member is on it, which, while not as useful as the recon bonus, but can be used for nice foward spawning in enemy trenches. Engineers just use the defeault spawning system. Assaults get the chemical barrages which are snynomous with WW1, which are really great for area denial and blocking LOS, while Engineers get smoke screens which eventualky can be upgraded to incinderary strikes. however, Engineers truely shine in that they get a special heavy weapon which is totally unique in function, and an MG on top of it. For the Entente its a shotgun, and for the Germans its a flamethrower. Personally I love the shotgun, it gives you almost garunteed one hit kills in close range situations and the reloads are painless compared to rifles. Flamethrower feels a bit more niche, but its good at area denial if nothing else. Assaults get only rifles (and a SMG if youre German), but tet lots of grenades and better melee options than other squads.
A good team compisition is a recon, a basic, one assault or engineer, and then the fourth squad can be really anything but a second recon (although a second basic or a sentry would be the gest to round it off).
One last note from soneone who loves playing as MG: Entente MGs tend to have more reserve ammo but smaller magazines, and can be fired from the hip unlike most German MGs (although the actual benefit of MG hip firing outside of trench raiding is... dubious. Always deploy to fire if you can, unless mobility is more important than accuracy and actually hitting your target). The German MGs, meanwhile, I feel are more accurate, higher ROF, and resultingly a quicker TTK. Both have their tactical uses, but playing MG you need to realize you do different things depending what side you are.
EDIT: AND PLAY NCO!
I know, youre stuck with (mostly) pistols and thus you cant really go shooty shooty yourself, but they are the most important of the four squad roles, always. They can set orders (which gives passive buffs if you are are near them), call barrages, and are usually estensial for getting foward spawning to work (except for recons basically). Any squad that doesnt have an NCO attached to it is estensially worthless on offense since you will /always/ spawn back in your trench, which means you exert /no/ physical pressure
Plus those barrages are reslly powerful, fun, and inflate your K/D. Whats not to love about that?