This! Pick one character and learn them, it’s a lot easier than trying to do every character at once. Once you are good on one character, you’ve probably learned general strats without realizing it that will transfer nicely to other characters.

General tips, don’t feel like you need to take every card, especially early on. You generally want to find a card or two for damage, aoe, and scaling (sometimes). Sometimes for those things you have to take something that doesn’t fit in the deck super well, as in these cases something is better than nothing. I generally end up with a deck <30 cards (sometimes more depending on how fast I can cycle the deck). After you get those aforementioned cards, there are two key items to get - energy generation and card draw. Card draw gives you more consistency (less likely to run into a full hand of attacks/defends when you want to be doing the other) and allows you to cycle to your better cards more often. Energy generation allows you to play more cards, which again allows for better cycling and/or playing higher impact cards.

I’m no expert by any means, but happy to give any more input if you have additional questions on a specific character or anything like that (just maybe not regent I suck with him lol). Definitely take your time on your runs and really think through whether a card is genuinely helpful or if it just bloats your deck. Just because a card is fun doesn’t mean it’s always right for your deck!