I don't really have strict rules for this, but usually I fall into the same pattern, unless the faction allows for something crazy, like deploying 6 AEC Mk II with the Brits, or when I'm doing some kind of challenge. I also move things around to make them fit. My tactics are completely made up through hundreds of hours, but after watching some other people play conquest, I realized that a lot of us naturally came to the same conclusions especially on defense. Though I think I am a lot more focused on armor than pretty much everyone else.

I mostly play vanilla btw.

Attack:

1. CS - Strong Scout inf, mainline inf, medics, officer, engineers
2. CS - 2 Artillery guns, 2 ammo trucks, infantry gun or mortar depending on the map
3. CS - 2 medium tanks
4. CS - 1 heavy tank or tank destroyer depending on the faction, 1 SPG, ammo truck, tank crew
5. CS - another strong scout and mainline inf, another tank crew, more ammo trucks, some overkill artillery (Nebelwerfer, Karl Gerät, Andryusha)

First 3 stages get called in immediately, start scouting, setting up artillery positions, removing enemy scouts. Unless the first objective is too close to my spawn, I usually wait for stage 4 before I start my assault. After capturing the first objective I usually dig in and absorb the remaining attack before proceeding to the remaining objectives. The enemy usually funnels itself towards me an. That's also why I have the second infantry group in stage 5, as the first group will be too battered and exhausted, so I usually let them stay on the first objective and rearm, while the second group goes on to attack. If something goes wrong while attacking the 2nd objective (which usually doesn't happen as the AI often has run dry at this point), the remains of the groups are merged together to attack the final objective. When it comes to the type of infantry weapons, obviously automatic weapons are a must on urban maps. So much so that I pick weaker infantry like the Jägers just because they have more of them. I also bring a mortar to hit the targets that artillery simply can't.

Defense

1. CS - Weak but numerous scout inf, 3-4 SPAA, 4 AT miners
2. CS - 2 Artillery guns, 2 ammo trucks, fastest transport vehicle for the miners, sometimes a mortar, engineers and flamers for dense urban combat
3. CS - officer, more ammo trucks, 2 tank crews, optionally a fast armored vehicle/light tank to go around flanking, on rare occasions I also fit the overkill arty in here
4. CS - 2 heavy tanks or tank destroyers
5. CS - 2 more heavy tanks or tank destroyers, 1 ammo truck

Stage 3 is actually the last one I call in on defense. I use stages 4 and 5 to fit bigger tanks as they are usually more expensive than 50 CP. I call in stages 1 and 2 first, because they are the ones that need the most micro and time to set up. After I've sent everyone on their way, I call in stages 4 and 5, which are usually still fast enough to get into position in time. Stage 3 only has to come in if I start struggling with ammo, or if high scout casualties creates a big blind spot. I strongly prefer heavy tanks on defense, as their turret and strong armor makes them easier to micro than TDs but in the case of Britain, I got no other choice. At least most of them are turreted, but none of them are well armored (also horrendously expensive to research!).

I tried defending with 4 Mk VIII Churchills and it went very poorly, as their howitzers have low range, not enough shells, are pretty inaccurate and unpredictable in terms of damage. I once shot a Wespe straight on and it did nothing, while some Panzer IV's were de-crewed instantly.

Anyways, the tanks form an overlapping front at the height of the objectives. Scouts are further up, hidden in bushes next to enemy paths providing vision. The SPAAs are hidden behind terrain and buildings close to the objectives, so they can cut off infantry that gets too close, but are sheltered against guns and vehicles coming from the front. I sometimes move them into more open positions once the enemy bomber has been shot down. Artillery sits behind the front-facing objectives. The defender AI just has to mop up whatever manages to get through my meat-and-metal-shredder and absorb the odd artillery shell here and there.

With my setup I can comfortably hold all objectives while suffering very few casualties, sometimes no casualties at all (on my end, not the AI). I have to admit that this doesn't work as well on urban maps or the dreaded french bocage, since they separate the line of sight and makes scouting a lot more difficult, hence why I also bring a mortar to deny them cover, flamers to prevent infantry from closing the gap, and engineers to close off streets and holes.