Practice in front of fellow developers.
Remove slides when you're getting close to your presentation, don't add more.
Make sure that you have a a good conclusion or summary.
Get feedback from the organizers after submitting your proposal.
Details are alright if you're allowed a long time slot.
Get feedback from fellow developers before submitting a proposal.
Cut everything you can consider a side note or an aside. Don't go into too much detail.
Give the audience just enough information to peak their interest. Don't delve on the details.
Consider referencing resources to learn more about the topic.