No character will fit the stereotype 100% all the time. Most will never fit it 100% - no matter how on brief your concept you are still playing an individual with their own personality and it’s still you playing them. Everybody slips.
I’m also new - not just to Empire but LARP in general. Decided on playing a Changeling as it gave more scope for character development - and according to my partner, summer suits me 
So, as someone else who struggles with small talk in real life, and being fairly quiet in general, I was aiming high (mainly to bring me out a little). It kinda worked, although I lost the consistency with speech a little, and wasn’t that talkative/social for a Changeling - my excuse is I’m still finding my feet in the whole thing 
Now I’m more familiar with how it works, I should hopefully be able to work on that.
Other excuse: Lineage varies from character to character. The stronger the lineage, the more of those traits your character will have, although there’ll always be a bit of human in there somewhere 
If you are having trouble with small talk, get a job in one of the many IC businesses. People approach YOU, then you have the choice as to how to respond. Makes it easier, as there is (almost) set lines. ‘Would you like a drink?’,‘So, What are you trading?’ etc.
I’m not a terribly good role-player, So i tend to stay human, and play my own personality with maybe a trait or two ‘Up to eleven’ such as arrogance :p.
I have found that having an ‘End game’ can contribute to how you personality is. What will happen to make you say ‘I’m done’ an re-roll?
Could be a 1 year plan, could be 2. It might change (Mines changed 3 times). But have a target. If you are aspiring to become a general/archmage/empress you will need a certain attitude to be able to get that - Leadership qualities, shoutyness etc, If you are going for more of a trade house, have you a target amount you want to hit? you’ll need to be forward and active.
A player led game will ALWAYS change while running, so don’t be afraid of changing your goal.
I also find it keeps the game interesting. As a very First-Empire problem - I found that I have too much money. Not enough to challenge anyone for the bourse seats, but a lot of walking around money. There is only so much Tea, Cake and backrubs a man can buy! Although everyone will willingly take it off my hands, and also I feel that having earned said money, I should use it for something SO FUN and pricey that no-one else can do it.
So the personality changes again.
Ooh a last point - many many people have told me that previously they have died on (say) the saturday afternoon of an event, Then made a throwaway character for the last couple of days. Because they are unafraid of dying they take more chances and are more relaxed and end up having more fun… and the character sticks. So It may be worth not thinking about it too much