Frankly, I look at specifically character traits I want to play in someone and then look to hobbies. It can be easy to flesh out a character's personality first based on either yourself or just 'what sounds cool' before molding the backstory around it. Alternatively you could start as a bland no interests baby and morph it to their life experiences.
Haven't ever tried this so I suppose it's a personal thing. Usually I just remember them and occasionally bring it up in conversation with the player.
Personally I go in with absolutely no expectations. Even still, I feel this happens to everybody eventually, and sometimes you have to find other things that weren't even planned from the start. For example, my concept for my current main (Monkey Peregrin) originally started out as a travelling bard without and real set home. Before I knew it, he was adopted by a long line of tinkerers and became one himself. Now, he's a Farseer Shaman.
The point is, don't always try and railroad you're roleplay experiences, and let them more come naturally.
I don't think I've ever actually started with a conclusion, no. I know for most human players and such they have to stick to the whole "Have kids, do this, do that" but as a Halfling player, I have never really seen the need to plan things out. I find it much more enjoyable to fall into things.
No powergame no metagame lole.
But seriously, don't have an answer with that one. If you fail at a persona, I would just pick it up and try again or go a different route entirely.
Also, for a final note, the more random personas the better. It gives a lot of depth so you don't get burnt out easily. My two current main personas are a Shaman Halfling and an Epiphyte who wants to conquer the world.