With another round of "conference season" and Call for Papers starting up, there's some timely advice from Lorna Mitchell with some suggestions about submitting a talk to the conference of your choice.
I've been a conference speaker for a lot of years now, which doesn't make me an expert but it does mean that people ask me for advice pretty regularly! With the Call for Papers open for PHP North West at the moment (awesome conference, first weekend in October, CfP at http://conference.phpnw.org.uk/phpnw15/call-papers/), I've taken this question a few times. Here's my advice in a nutshell.
She shares five tips that she feels can help you make for a better abstract and submission including writing it down before submitting and asking for peer reviews before hitting that submit button. She also links to a few other helpful resources that can provide even more tips to help you even once you've been selected.