Here goes.
Tips for playing as Union in July campaign
1. Before winter:
- secure Missouri. You can send cavalry to seize Springfield and Fayeteville. Both have depots, so they will be fine during the snow. Rebs will lose two important towns and two depots.
Price should be easily delt with, once he is cut of from his supplies.
- secure all your holdings in Kentucky and bordering states with militia. Bowling Green is a possible death trap for you if you don't secure your rail lines. Build few depots; one in Bowling green and one or two extra ones in bordering states. Get Lextington, KY. That should be enough for first year.
- seize HF and Winchester. Possibly take Manassas but that is not so important for first few months. Settle down during the winter
- build up your river and sea fleets. Try to blockade few ports. One of theimportant ones is Richmond. It has only one exit point and it is easily blocked. Try to find some similar ones.
- try to take Norfolk. Even on the account of losseing ft. Monroe. Norfolk is a strategic town with a harbor so...
- secure Pensacola with one division. If there is time, try to take Mobile. Strategic town with harbor. Great for repairing your Gulf blockade squadron.
2. During winter
- don't call for volunteers during winter. Larger your forces, larger the hits you'll take. Place your forces into towns with depots. Try to have medical units and supply wagons with them in order to reduce the damage from harsh weather. My suggestion is to buildup a fleet during winter time.
3. Army matters
- 1st army - Manassas - goal Richmond
- 2nd Army - Bowling Green - goal Nashville
- 3rd Army - Rolla - goal Springfield and west
- 4th Army - HF - goal clear Shenondoah
Mistake I usually did was to build an army in Grafton. That army IMHO is a waste of army HQ as it has to march quite a lot and there are no strategic towns nerby. It is ok to build it as 5th or 6th army but not before.
Also, pay attention to your 3 star generals. If you know when and where they will appear send them to locations where they will build their armies.
I find it ok to have armies with Banks and McClellan as I always attack when strong in numbers.
That is about it. Hope it will help.
Godspeed
P.S. feel free to comment

Forrest said something about killing a Yankee for each of his horses that they shot. In the last days of the war, Forrest had killed 30 of the enemy and had 30 horses shot from under him. In a brief but savage conflict, a Yankee soldier "saw glory for himself" with an opportunity to kill the famous Confederate General... Forrest killed the fellow. Making 31 Yankees personally killed, and 30 horses lost...
He remarked, "I ended the war a horse ahead."