Okay so.
This is a big problem in all writing, which is why in books you will sometimes read a Point of View character literally staring in a mirror and describing themself. Looks are a hard thing to describe in fiction without being awkward, and often it's unnecessary anyway. Personality matters more.
That said, if you don't provide a character sheet and you want the other player to know what yours looks like, there are some tricks for this.
1. (BEST) Describe your character doing something that includes their physical trait. For example, a guy who is about to enter a battle who is carrying a sword and wearing armor might loosen his sword in his scabbard, and he might adjust the way his armor is sitting. If you want to get more detailed that's also possible, but can come across as fake or annoying.
eg. He tensed, hair rising on the back of his neck. His thumb ran over the woven steel of his rapier's hilt.
Not super elegant, but still better than saying 'He was carrying a basket-hilt rapier'.
You can have fun with this, and apply it to a bunch of things. For example a big, tall character might duck through a door or turn sideways to squeeze through a crowd. A gorgeous woman might catch a teenage boy staring at her. A fat girl might tug her shirt down self-consciously when it rides up. These do the job and help the reader discover the personality of your character.
2. Meet a family member or someone whose looks you can compare to your own character. This can come across as really hack, but can work if you're careful.
eg. Miro's sister, she'd always thought, was like a stunted, mutant version of herself. Hannah's black hair was a wild tangle, unlike Miro's sleek perfection. Her eyes were huge and never blinked enough. They reflected the light around her on inky pools, like angler-fish lanterns in the abyssal depths.
In this Miro comes across as a pretentious narcissist and her sister as Eldritch-insane, but, hey, we got both hair and eye colour in there and implied Miro is very neat and prim.
A note here about narcissism: You have to keep in mind that whenever you describe something it will come across as your character thinking about that thing. So if you constantly describe their appearance your character will come off as self-absorbed. In this case Miro is self-absorbed, so fine.
3. If it's appropriate to the situation, your character can do a stock-take of the stuff they're wearing/carrying. For example if someone's entering a party or about to take a road-trip it's pretty normal to start thinking about clothes and looks.
eg. Why the hell had he come here? Ivan tugged his t-shirt, sidling through the glittering crowd. He'd come straight from work, still had paint spatters on his boots. When he thought no-one was looking he licked his thumb, scrubbed viciously at a white spot on the knee of his jeans. This was Miro's world, and he hadn't even shaved.
There are probably more tricks, I don't know. Anyway the main thing I think is to get value out of each sentence, because no-one likes to read a list of clothes and hair and eye colors in a roleplay (or in general). So ideally the description of the appearance should also tell us something about the character's personality and/or their situation.
Good luck!
