Need some help (platform game)

[Magicore]

Hello there.
I made a simple tileset for my new platform(metroidvania) game.
Anyway,I wanted to go with the simple and clean theme because im not so good in pixel art.

The tile:


The player(Kinda hate it but that what I could do):

(hands very small but you see them in-game)

Its "ok" but the game feels so empty and I cant draw any backgrounds / decorations, in that style anyway..
(p.s the whole game set underground in a cave. You fight slimes/skeletons/etc..)

So can anyone give me some tips or examples how to continue from here?

Thanks.

[YellowLime]

What are the cross-tiles supposed to be?

The player character has a nice 'personality' to it, but I would fatten up his legs so that any walking or jumping animations would be noticeable (also so that he doesn't look like a double-amputee pirate ).

The collar opening should be facing to the right, to make it read more like he is facing towards the right.
Right now, for some reason, it's facing slightly to the opposite side, giving the appearance of him turning his head to face something to the side.

Where to go from here? Maybe have some background tile(s). If the platforms are going to be dark, the rule of thumb is to make the background lighter, for them to contrast with each other and make the layout much more clearer than otherwise.