General rule of thumb, roleplay in third person. In script. That means write the way you would see in a book. Avoid using "I" and "you." It's too personal, confusing, and makes people feel weird. Instead, use the characters' names and/or pronouns.
❌She walks up to you

❌I walk up to you/them

❌*walks up to them*

✅She walks up to them

✅Casey walks up to Jacob

Avoid using asterisks(*). I can't speak for the rest of you, but I automatically assume any who uses asterisks to be a terrible role player.

The average (good) role players appreciates 3-5 lines of content. I've seen some people write entire essay-lengths in group roleplays, and while I think it's impressive, not everyone has to be like that. At the very least, just have enough for somebody to work with. If 75% of your replies look like this:

-"Okay," Jacob nodded
-"Yes," Casey smiled.
-"Mhm," Wendell agreed and ate.

You are boring, you are uninteresting, and I hate you. I had to say it. I'd have more fun talking to a brick wall. You can't possibly expect someone to come up with a fulfilling response to this. They're not gonna have fun, you're not gonna have fun, no one is having fun, roleplay dies.

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People need details and description, that's their ledge to jump off into their reply. Consider your Who, What, When, Where, Why, and How before your write a response. Describe the scene, where are they sitting? How are they sitting? How do they feel? Why do they feel that? Why'd they say or do the thing they just did? What are they wearing? It may seem extra but these details are important for people to connect with your character

Be careful though, to keep a balance between important and unimportant. Don't spend an entire paragraph explain what your character looks like and what they're wearing. It gives very "y/n, pick me"
Don't do this:
❌"Caroline entered the room, her pink Demonias clicking on the floor. As she sat, her beige plaid skirt flared over her crossed, thin legs. She flipped her auburn hair over her pink button sweater and looked around. The pink beret with pearls complimented her cute, soft girl makeup look on her delicate features."

Consider:
✅ "Caroline confidently entered, heels clacking on the floor with each step. She was very proud of what she thought was a well-put together outfit, a beige plaid skirt and pink sweater. She worked hard this morning to look presentable and hoped someone noticed."

This tells your character is confident, fashionable, maybe very organized and neat. Probably likes attention. Introduce characters by their personality, not looks, unless they have a particularly interesting or unusual feature.

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Don't wait for people to come to you. Approach other characters. Appropriately. If two characters are having a private/deep conversation, don't butt in unless it relates to you. If two or more characters are having a casual, open, public, then join in.

If you have a shy character that doesn't like going up to people, then make them approachable. What makes your character interesting enough to talk to? If they're just sitting around reading a book or listening to music, 9/10 they're gonna be left alone just like you would someone doing that in real life. Maybe describe the cover as being creepy or suspiciously suggestive. Maybe say that their listening to music noticeably loud. Tell me they're sitting with a straight face listening to the Thomas the Tank engine intro bass boosted. Entice me.