Be unique in everything you do in an RP

Have something mysterious about your character.  It makes people want to RP with you more, to figure out whatever it is

Have an in-depth character.  This improves your RPing skills simply because you KNOW your character

Take my advice (LoL)

Re-read your RP's!  Very important, although few people take the time to do it.

Download a free spell checker to use ( www.iespell.com )

Ask someone if you need help on an RP, or on increasing your skills.  No one is going to give you some tips if they don't know you want any

Be willing to accept any advice that any members give you on how to improve your RPing.  It isn't meant offensively

If you have an evil character... BE EVIL!  If you're an assassin, you wouldn't be seen laughing with a pretty little fairy.  RP's are IN CHARACTER and anything harshly said to a character isn't actually being said to the person in real life.

DO NOT have a mind reading character.  This is something that a lot of  people have, and I question their sanity.  Do you know how frustrating it is to be RPing with someone who can read your every thought?  RP's get shortened big time when you have to edit out all thoughts your character may be having

DO NOT have a perfect character.  This is unbelievably frustrating as well, and makes you look quite desperate.  It is okay to have really obvious and good traits, but everyone has to have, and needs, some flaws

DO NOT expect the other person to carry the RP on for you.  Add actions to it, make it a plot that's interesting

DO NOT bring out of character issues into your RP's.  If you are extraordinarily angry, don't let that affect how well you RP.  

DO NOT RP a person's character for them.  I've met people who do this before, and it is extraordinarily annoying...

DO NOT god mode while RPing, even in the slightest bit.  It doesn't have to be in magic, it can be in anything.  Let's say you bump into them... don't say they fall.  Never, ever, ever, do anything to the placement of the character you are RPing with, unless given permission

DO NOT be annoying... seriously... sometimes it is okay to be a hyper character who bounces off the walls, but if you try to do this 24-7 then you'll notice everyone runs when you ask 'anyone want to RP?'

DO NOT be an expert at everything.  It gets very annoying when you're RPing with somehow who can cast a spell for everything, with no apparent side effects

DO NOT join more RP's then you think you can handle.  If you join more then you can easily reply to, you'll see your posts slipping into the unknown realm of bad RPers... simply because you have so many to write.