Well I had a link to my other post in one of the previous posts, but apparently it disappeared. Would have responded sooner but the search function on lucasforums wasn't working so finding the other thread was a bit of a pain. Anyway, I'm just going to quote it in here to make it easier:
I usually get to Echo base with pretty much everybody intact. If you're not doing so already, stick your troops in your AT-ATs to keep them safe; you really shouldn't need them for the first part. Use Veer's regeneration to the utmost; keep him in the lead and pull him back when he needs to regen. I usually use my smaller mechs as close quarter support for my AT-ATs, so mounted troopers and the like can't get too close. Another good tip, if you don't mind micromanagement, is to limit how many AT-ATs are firing. Use a couple headed by Veers to take out towers, etc and keep a couple in reserve to fire on mass groups of people. That way you won't have every AT-AT stuck in recharge mode when you really need them to blast hordes of troopers/mechs. Keep in AA troops in your AT-ATs when you're not using them, and simply pop them out when you're facing speeders.
As far as as advancing is concerned, you might want to keep to the edge of the main path (usually to the south). This will allow you to pick off the individual unit-producing buildings early and prevent you from getting hit at both sides...
As you can see, this message assumes that you're making to the AT-ATs intact (believe the original person who I was responding to was getting to the AT-ATs ok). If you're having problems getting to the AT-ATs I'd suggest using your longest-ranged units to scout (probably either mechs or grenadiers). I believe the longer ranged units should be able to destroy the light turrents on the initial run south without getting hit. Use them to draw out your opponents when you hit the buildings at the southern end, and take out what you can at a distance, using your mounties to destroy units like mech destroyers and grenadiers if necessary. Drop the pummels down the right side to eliminate buildings and suppliment them with the mounties...