How do you play a roleplay character?

Lyserus

^This
I just recently created a set of characters based on Planescape: Torment
I love them, however, I find myself constantly thinking about what fits their characteristic and having a hard time deciding what quests should they do

Do anyone ever had the same feeling like I am feeling? Any tips?

Lysette

That is the whole point of role playing - that you immerse yourself into this character and decide from his/her perspective, suspending your own personal view on things, and just play it out from their perspective. if you have a hard time deciding what quests they should do - that is not the question, the question is, what kind of quests do they want to do and do they want to do quests at all - or just help out in certain specific cases. just start playing without opposing a goal on them - you will see, that they will find their own way over time - if you play them out just using their perspective not yours.

Start with simple things - they need to eat and drink - but they need money as well to buy it - so either they need to find a job or some activity to earn some money. A very basic start, but from there just decide from what they experience. They need some shelter too, so get an inn-room. That room is empty and they certainly don't want to sleep on the floor for long, so they will like some furniture and eventually some nice fluff as well to make it cozy. Start with such things and see what game play will be created by caring about those needs.

Danikat

This is why my roleplay characters are tailored to the game they're in. I've had to give up on some ideas because they didn't fit the game - either the kind of choices they'd make weren't available or their personality wouldn't really come through and that made them boring to play. (Or in some games the choice were available but were boring - like playing a lawful evil character in Neverwinter Nights - pretty much your only option was to demand a bit more money from people you'd helped.)

I do have one character I've been using in most western RPGs for about 20 years now, but she changes slightly in every game (not just her race, class etc. but her backstory and some elements of her personality) then those changes influence how I play her in future games. She's not quite the same as she was 20 years ago, she might not be older (unless she's an elf or similarly long-lived race) but she's grown as a person.

But in general yes, it comes down to being aware of who my characters are as people and choosing quests and actions based on that. For example some of my characters will never join the Thieves Guild or the Dark Brotherhood because they're morally opposed to both (and some are frankly terrible at any form of subtlety) and I'm ok with that limitation. One will never go to Valenwood (or will have to be very careful about where he goes if he does). Sometimes I change their mind to suite the game - for example my khajiit said she'd never go back home after leaving, then when Elseweyr was released I decided 'home' meant specifically the area around Torval where she grew up (which is conspicuously absent from the game). If that area is ever added then I'll decide enough time has passed and she's willing to deal with it.

It helps that most of my characters are somewhat impulsive so their default is to accept a quest and they'll only decline it if it's obviously not something they'd do. I tend to think you'd need to be that sort of person to be an adventurer (or otherwise end up in the situations that start TES games and be offered these quests) but it means I only decline a quest if I'm sure it's not something they'd choose to do. If I'm not sure what's going to happen then neither are they and yes it might go badly but that's life.