I'll shield you!

Try to get Unflappable, Armored Vest, Electrostatic Armor and Nerves of Steel on the table as soon as possible.

Unflappable - gives extra cards to play or discard to ready Captain America using his personal action. Armored Vest - makes sure you don't get too much damage so you can use Unflappable. Electrostatic Armor - slowly but surely deals damage since it's combined with Cap's Shield (retaliate 1). Nerves of Steel - It never hurts to have a permanent resource on the table.

Try using events like Expert Defense and Desperate Defense to make sure you don't receive any damage. Again, this helps you gain more cards with Unflappable, and therefore you don't have to ever switch back to alter-ego.

If you do have to switch back to alter-ego, make sure you are already ready to play Nick Fury to do whatever is needed. However, I would recommend using him to draw 3 cards to prepare for upcoming attacks. Also be sure to be ready to play Iron Fist to start damaging and delaying the villain. Allies will be easier to play in alter-ego since Cap lets you pay -1 for them and you can use The Power of Protection for them, since most cards in this deck are cheap enough to not have to use double resources on them.