The tips I got were as follows (and they worked for me):
1. ATFQ - if it asks for AN example, give AN example, if it asks for 'evidence', give exampleS (plural). Failure to do this means lack of attention to detail = bin.
2. When you answer, make sure to put (1) what the situation was, (2) what YOU did, (3) what the outcome was (who benefitted, how much, how many people made happier, how much money saved, etc)
3. For the motivation bit, refer to BA's documentation. Phrases like 'world's favourite airline', 'best in the world' may sound cliched, but they love that !!!!! apparently.
3. Get it right before you put pen to paper. Use a word processor first. Start with brief notes and expand as you go until you've got a page full without woffle, play with word order (for hours if necessary) til it reads like poetry. Spell check, grammar check, double check. Read and re-read it. Get your mates to read it. Get your dad, your girlfriend, your tutor to read it. Only then put pen to paper.
4. Don't lie. You will get found out, as they will refer to the app form at interview. Also for this reason, know what you wrote. After you've transcribed in your best copper-plate onto the real thing (don't drip sweat on the page, it smudges the ink), go back to your Word document and make sure it's identical. Then you've got a record of what you put down.
5. Deep breath, off to the post box. You'll get a 'Thanks' letter within days, invite to aptitudes within a week or two.
6. Check the Wannabes Archive for aptitude info and final board tips and you're on your way.
WGW