Send out as many cheap units as possible at the start while continuing to push your opponent. Resource generation will be low at the start of a match. Your opponent will have greater difficulty fighting back after you are at an advantage. In campaign levels, you can preview what types of units the enemy has starting a battle. Red units are strong against Infantry. Green units are strong against Recon. Blue units are strong against Tanks. White units are strong against Air. Wait at the start of a match until your opponent deploys their first unit. Then deploy a type of your own that is strong against that type. Continue doing this after each turn. You will eventually be able to push in. After you reach level four or five of resource generation you should be able to clear it.