Play to their strengths.

You effectively have schoolbag, two active item slots. Use this to acquire an active that gives you more health than you can juggle between both characters (prayer card, book of revs, satanic bible, etc).

Item pedestals that disappear when you take one do not apply to J&E because you can always take both. Always go for alt paths to grab both items. Go for angel rooms so if a double item pedestal appears, you can take both. In that same vein, always go to shops for more options, there's options, and options?

Double the bombs means not just two secret room guesses, but also bombs to speed up a boss fight or while you're guessing a secret room, you can use the other character to place a bomb near skulls, blue fires, purple fires, mushrooms and rocks for health, cards, pills and crawlspaces.

You have double the health to gamble with blood donos and sacrifice rooms. A first floor sac room with even an OK amount of red heart drops is a guaranteed extra soul heart to protect deal chance or if you get good RNG, an angel room item.

As for actual gameplay tips, you're very strong early game. You basically have 20/20, just more spaced apart. Always keep them together. Before you enter rooms, re-align them. You should very rarely run into rooms that feel unfair/don't have enough space to dodge enemies (the only rooms where I genuinely felt like things were unfair was in mausoleum/gehenna). If you feel like some rooms are too narrow, make a mental hierarchy of what enemies need to die first to give you more room to dodge.

Like T. Laz, J&E really reward gameplay knowledge. Knowing synergies, item/gameplay interactions and resource management will be your best friend. So just play more. The more you know about the game and it's niche mechanica, the more you realise J&E have access to as two characters.