Get a good NPC army leader unless your noble has excellent stats, which is rare among the French. IF you aren't sure which of your NPC's have excellent combat or siege stats, you can analyze each NPC in your employ from the Family Matters menu, by using the "K" or "analyze NPC" option provided there.

Do not ever get caught in a siege over reset unless you are sure you won't get hit by a relief army, are sure you can win that battle or at least not get completely destroyed. Remember sieging costs 10 days per attempt. Sieging can take a lot of time, so watch you days left carefully.

Rather than recruiting and disbanding each season, you should be working in small teams of 3-5 nobles. One noble will act as the collection agent, and pick up transferred troops to hold over reset. Larger armies can avoid combat by setting the Standing Orders to retreat, and instead of spending precious days recruiting, you get almost all 90 days for sieging. It takes some coordination, but unless you plan to let any fief with a keep higher than 5 stay in English hands, some planning and team coordination is necessary.

Avoid army versus army combat unless you are fairly certain you will win. As French you will most likely lose unless you have a 2:1 superiority in men and a good general, which means either your PC, or an NPC you have appointed as army leader. English armies are, generally, twice as potent than any others on a man for man basis.

Having other NPC's traveling with you has little effect at this time. At best they add a few men to your army count. If you have a very small army, of under 300 men, a dozen or so NPCs will increase your combat strength by 5-10 percent. However, as a general rule, there's no real need for all the extra NPC's unless you like to spend the cash for them. One thing to consider as well is this: when in this combat, the winner usually captures most of the loser's NPC's. Once they are captured, you won't know who has who, as one strategy the enemy often employs is to transfer captives to other members of their team. It is therefore advisable to keep a list of who you have so you can be sure when you ransom them that you got all of your retainers (NPCs) back.

Another tip: Always place your army in retreat mode when you are not actively attacking someone. If you are attacked, in most cases you will retreat without fighting and they will have to spend precious days to track you down again. Losing battles means at the very least you take a stature hit; it could also end up with you wounded, captured or killed.

Lifting sieges is basically an army vs army combat.