My take on this topic:
1. Spontaneous interaction is what makes RP feel alive. So be sure to respond to what your partner is doing and give them things that they can respond to, too. And let things happen in sequence. Don't tell your partner that her nipples are hard. Tell her how much you like the feeling of her nipples in your fingers. Then, if she tells you that that makes her nipples hard, tell her how much you like feeling her nipples grow hard in your fingers. Stuff like that.
2. Write concisely but expressively. Unlike some kinds of writing, the extensive use of adverbs and adjectives can be effective in RP, because you should be describing what you yourself are experiencing. But don't write so extensively that your partner has time to go get a cup of coffee, either. An example of a sentence pattern that I use a lot is "/me looks deeply in your eyes while softly running my hand up and down your silky smooth back." I like this pattern, because it's not too long, but the two verbs describe the actions I am performing, while the adverbs and adjectives convey what I am feeling as I do it.
3. Don't worry about minor errors in spelling, grammar, or punctuation. Timing is just as important as content, so keep the back and forth going at a lively pace. I do agree with Athene, however, about making the effort to spell words out rather than using abbreviations.
4. Don't worry about mixing the first person and the third person when using the /me command. Yes, the sentence starts with your name, which in the English language places it squarely in the third person. There are many languages, however, in which it is perfectly acceptable to refer to yourself using your name or otherwise talk about yourself in the third person. So don't waste time agonizing over whether you should write "/me takes your hand in mine" or "/me takes your hand in his(hers)." The difference is not that significant unless you are RPing with a grammar Nazi.
5. When changing sex poses, try to sequence the changes naturally and provide a short description of what you are doing before offering the next pose. Sure, it's ok just to offer someone an oral sex pose, but it's even hotter if you describe how you "kneel down meekly in front of them and look up at them longingly" just before you offer them the pose. Shit, did I just give away my subby side?
6. mmmmmm, ohhhhhhh, fuuuuuuuccccckkkkk, sheeeeeeeeeeeeettttt, etc. are ok sometimes, especially if you need a filler while you are thinking up your next action. But they get boring before too long, so try not to overuse them.
Anyway, that's enough from me. Hope you find this helpful.