love that game, I did play through the campaign on one of the harder levels, but haven't really done pvp.
saving is important especially when you are outnumbered and out powered.
I think there are 4 save slots so I used one for in base between missions and one for the start of each mission and two for in mission slots. (you have to disable autosave). that way you can try out a few different strategies. sometimes thinking outside of the box as allowed me to overcome overwhelming odds.