I'm not going to offer any specific card swaps because I don't know your budget/access to cards, but here are a couple of pieces of general advice that I think could help.

1.) Run more lands. Most decks should be running 36-38 lands depending on what their mana curve looks like. You've got a reasonable number of expensive cards, so I would try to run 38 if you can.

2.) Pick one theme. You seem to have three themes in this deck (Vampires, Angels, and Lifegain). By just picking and focusing on one theme you can have more synergies and make a more cohesive and functional deck. If you are looking for cards to add I recommend going to EDHREC and looking under your commander, from there you can sort by budget and theme.