Heyo, Simon! Understandable, if this is your first time venturing into rping, that you'd feel a little insecure about your skills. Do not fret or feel discouraged, this is a natural part of the process. Partners come and they go. Even someone like me who has been here for many years and feel pretty confident in my handle on storytelling, even I get dropped occasionally. It just happens.
If you truly feel like your skills might be the problem, then I'd recommend 2 things for your proposed problem: 1. read. Not joking. I used to write homoerotica in HS before I even knew what a prostate was and it shows in my old notebooks. Then I started reading gay fanfiction online and getting trashy romance books from the bargain bin at the used book store near my house. Stuff like Christine Feehan, because I liked the dark tone and vampire plots but there's plenty of options out there now. Sometimes reading all of that flowery language and gushy, emotional writing can give you a feel of the tone and details you want to go for. You can read it and either go "oh yeah, that's really hot, I like that!" or roll your eyes and decide when the writer has gone too far into "throbbing member/length and plowing fields" territory, picking and choosing from the text what directions sound best.
If that's a step you've already taken or you're in more of a hurry to "get good", then, another thing you could do to find the right words, if you already have them and can't bring them to mind, is use dictionaries.
My favorite is
http://www.onelook.com/ It's a collection of links and search engines that all tie into dictionaries that are available online. Not just reg dictionaries either. You search for a word and it'll bring up entries available on medical, architectural, mathematical, baby name, slang, etc. dictionary sites. So, you get a pretty well rounded view of what the word you're looking up means. But it's also useful for finding a word that you don't know but are looking for.
Like, you can't think of the word but you know how it starts, just put in a search for "sh*" without the quotes and it'll bring up words that start with "sh". Or how about, you know what the definition of the word is, you can use the Reverse Dictionary option, which allows you to type in words and bring up a list of words that fit those descriptions or have those words in their definitions. Or, let's say you're looking for a word like "chained" but NOT chained, you don't want chained for the spot you're looking for, you need a word that you can't think of but you know chained is very similar to it. Look up chained in the regular search bar and go all the way to the bottom of the page of entry results. you'll find a little link that says "Words similar to chained" and "Words with chained in them". That will bring up lists of synonyms that you can click through and see if the word you're thinking of is in there.
Also, there's
http://chir.ag/projects/tip-of-my-tongue/ as well, which describes the exact same functions except it's specifically for that. I personally, find that site to be a bit lacking, though, as far as searching for something and finding options to choose from, because I'm a very broad searcher and my memory will often make really vaguely related connections, so, more options for definitions suits me better than a focused approach.
Anyway, good luck, hope these help. If I had more time and patience, I'd help you out with the personal tutoring thing. Even still, the best I can offer, rather than subjecting you to my tyrannical teaching method, is to suggest you read. Read like a fiend. Replicate. :thumbs up: