I find that as the AI tends to use a "rush everything at your landing spot" tactic, it's wise to land cheap soldiers first. Combined with the AI's tendency to mass artillery, I rarely even waste my money on the more expensive units such as T4's and ATAT's.
Instead, as Rebellion, I use Obi-Wan, Infiltrators, Han/Chewie, and a mass of Rebel Troopers and Rocket Troopers. I scout with Obi-Wan or Han, as they absorb more damage, and have useful skills to deal with new situations emerging from the Fog of War. Behind this scouting group, I slowly bring up my Infantry Mass (walking together), and finally my other heroes, and Infiltrators.
A lot of the time, if the enemy does not have a mass of Arty, I don't even send infantry, just Infils, Han/Chewie, and ObiWan. It's a hell of a lot cheaper, and you need to heavily micro land units anyways. Chewie steals the big enemy craft, Han EMP's the others, the Infils Thermal Detonate them, and ObiWan heals and protects from infantry with the Infils. It's damned cheap, and rarely fails me.
As Empire, it's a bit tougher. You don't have a hero like ObiWan who can heal quickly, and you have no rocket troops. In that case, I mostly rely on Vader, and huge hordes of AT-ST's and Stormies. Once again, because it is cheap, and losing these units aside from Vader means little to nothing to me. If one attack fails, I can easily afford a new army and just Bomb the hell out of the strong points or masses of units which beat me before.
I find Land Battles are infuriating, as units are countered entirely TOO fast, and you end up wasting huge amounts of credits if you look away for a few seconds: hence my cheap, hero-centered armies.
"we have an agenda, a character assassination agenda, assassinating characters is what we do for a living" - Sukkit