Check out table 5-5 in the Dungeon Master's Guide, the table of One Hundred Traits.
It's meant for NPCs, but I encourage my players to roll on it three or four times for their characters. Feel free to ignore your rolls if you don't like them and roll again, or just pick out some traits.
It's a good way to get started.
The next thing I would do is write up three short paragraphs describing:
1) Personality (use the traits you rolled up to help)
2) History (just make up places and people)
3) Appearance (a good description, the kind you will give when your character first walks in)
It probably doesn't matter to you as a player, but as a DM, I give my players a 100XP bonus for each of the above paragraphs at the beginning of a campaign. (and would probably increase that for characters higher than 1st).
Other roleplaying tips:
- Use a different voice while "In Character". Everyone should instantly know whether you're speaking in character or not.
- Don't be afraid to ham it up, it's fun (but let others have a chance, don't hog the DM's time)
- Stay In character. Instead of saying "I tell the orc I'm really mad.", yell "You godforsaken hellspawn, I'm going to hack you to pieces!!"
- Stick with your character's personality for a long time - don't change it frivolously. That way, when something significant happens, and his personality changes because of it, it will be meaningful to everyone.
Roleplaying takes some effort and is learned over time, but is well worth it.
If you post your ranger's stats, others might have some additional advice.