Summer Month: 2 
Day 
1) the ideas
2) how would the Rp turn out?
3) POLLS!
4) Advertisement
5) what kind of Rp are you looking for?
6) Sign Ups?
7) creating the thread
Ok, now for the detail:
1) The Ideas
Think of an original idea. I tend to come up with my rps wile I am swimming laps. Think about the theme, cats, dogs, wolves, shifters. I also come up with rps in my weird fantasies. Try to think of multiple, then you could choose your best one. Try not to copy other people's Ideas. I found a Sign Up that was at the very back and no one had signed up for it. I asked the person if I could copy the idea(because I loved it!), they said yes. I created the sign ups and people came and signed up. The Rp is still going strong today.
2) how would the Rp turn out?
Will this rp "die out"? I say "die out" because no one posts replys any more. It dies out or looses interest. Will this happen to your Rp quickly or not? Are you looking for a long term Rp or a short term.
3) POLLS!
I always do a poll when I am going to create a Rp. That is why you need to come up with multiple ideas. I do this so I get other people's opinion. So, you don't end out not never getting to rp. I usually try to get to 50 or so votes. If you get a tie or two rps really close you may consider creating both.
4) Advertisement
Advertise, Advertise, Advertise. You want people to join right? Advertise your poll and your Rp. It always helps. If you want a BIG group this is crucial. Small group, eh, not really needed. The title also advertises to people looking to rp. Try to find a good title. For my soon to be Rp, The Disappearance, the title is mysterious and informational. It tells you it has to do with disappearing, but it doesn't tell you everything. But you want to stay away from titles like, Dog Rp. Yes, it tells you that it has to do with dogs, but this title, The Dog, tells you it has to do with a dog too, but it tugs at people's curiosity.
5) what kind Of Rp are you looking for?
You have found an idea, asked for people's opinions, and thought about it. You now are creating the Rp. I always put rules in my Sign Ups. I always like people that right a lot of information. I don't want, bob walked to the park. He ate a sandwich. I like a good and juicy paragraph. So, in my rules I put 4+ sentences. I would go 6+ sentences, but if two characters are having a conversation, it is hard. I also put, have good grammar and spelling. I don't expect people having always correct spelling and grammar, but I would like you to spell your words, put periods at the end of your sentences, etc. so if you are looking for people who wright 2+ Paragraphs, state that you must be able to write 2+ paragraphs. If you want people that wright as little as possible so you don't have to read that much, state that.
6) Sign Ups?
Sign Ups are great! I always do it. Then you know who everyone is and you can control the kind of people that enter your Rp. Don't be afraid to say, not accepted. I can't even count how many times I have said that. If in your rules, it says, "you can be a dog only if you play a cat as well." And the person signs up as a dog and doesn't have a cat. You could say, not accepted, please read the rules.
7) creating the thread
Put good info at the starting page of your thread. I usually put the character list, maybe the rules, and any other needed info. I also pm everyone who signed up for the Rp. Then they know the Rp had started. Once I poped into a Rp when they where on page 88 and I never knew we already started. I do this to take the stress out of people's lives.
I hope these tips/steps help you out in making the best group form Rp.
~The Inner Dragon
