I sucked at RP when I was new here, I'd like to think it became better eventually, but I've always struggled with knowing what and how to RP.
I personally have always found it easiest to base my RP on my race / guild choices. So if you want to get some help with RP there are some guilds and races that probably are easier to RP than others.
Ogres is probably the easiest to RP, since the race and guild guild itself forces you to RP "big and dumb" whether you like it or not.
Although I would not recommend ogres until you become a more experienced player. It's tough race to play with some big benefits but also many drawbacks.
Hobbits, kenders and gnomes also give you a lot from the start. Kenders are for example usually carefree creatures out looking for adventure with a smile on their face, and an interest in shiny things and what other people have in their pockets. Hobbits, well anyone who has read or seen the movies probably has a good idea on how to RP a typical hobbit.
A violent but not-so-bright goblin, or a stubborn dwarf are also typical RP choices of course.
A human I think is harder, as a you dont get anything "for free" with your race choice.
Same with guilds, if you pick one with an interesting and clear theme, it's easier to RP it than if you pick a guild that does not have a clear theme, history or goals, etc. These guilds have other benefits of course, but then you'll have to figure out the RP part yourself.
For example, if I say "pirate" everyone has an idea how a pirate is and acts. So it you get a lot of free RP help there. While if I say "mercenary" it's much more open for interpretation, and you don't get all that much RP help really.
I always think it's harder when you got too many options. "You can be anything!". Great, but _anything_ is a lot of choices. By narrowing down your RP choices with your race and guild selections, it might be easier to come up with who to be. Then you could of course go _against_ the typical RP cliché of your race, and play a grumpy kender, or a smart goblin. It's probably easier to start with the clichés though. Or so I have felt at least.
So if I were you I would probably think about which race seems the most fun to RP, then create a little background like Mirandus suggested, and when you know what race you are and where you come from, add guild RP to the mix.
That's my advice!