For the past few years I’ve been involved in the process of rating the proposals for a local event. Based on that experience, my number 1 tip would be to invest time to make your proposal concise and to the point. The proposal shouldn’t be too long, but also not too short. It should provide a clear idea of what you’re planning on covering in the talk.
By making a clear proposal, you’re demonstrating your ability to explain a topic. Think of proposal itself as a small explanation. As a reviewer, if I see a proposal which is not well formulated, I’m starting to wonder whether the talk itself will be understandable. My rating of the proposal reflects my doubt
Another thing I personally dislike is when a speaker submits a lot of proposals. 1-2 proposals per speaker is great, 3 or 4 is fine I guess, but going beyond that makes me wonder if the candidate is trying to get the slot at any cost, preferring quantity over quality. So my suggestion is to pick one or two topics which you think people visiting the conference might enjoy, and focus on making good proposals out of those topics. If you already have a stash of prepared proposals from earlier conferences, pick 1-3 which you think would be a good fit for the conference.
When it comes to technical topics, I personally prefer talks which are based on the speaker’s own experience, along the lines of “we had this problem, and here’s how we solved it”. It’s not a deal breaker, and it doesn’t completely influence the rating, but it might serve as an extra bonus. As an example, when I submitted my first proposal for a talk about Erlang, I named it “Erlang in practice”, and I stressed in the abstract that the talk is based on our own production experience with Erlang. I feel that this improved my chances of being accepted.
If it helps, you can check the Talk committee guidelines for the WebCamp Zagreb conference. Of course, bare in mind that different committees have different ways of thinking, and use different selection processes.
In summary, pick a good topic. Asking yourself the question “If I didn’t know about this thing, would I find the talk interesting?” is a good test. Once you have the topic, focus on making a good and understandable abstract. After you submit, hope for the best, but don’t take it too hard if you don’t get accepted. Conferences typically receive much more submissions then they have available slots (for WebCamp Zagreb it’s about 5x-10x), so rejections are something all of us experience from time to time. If you feel your proposal is good, look for other events where you can submit it. Also, IMO it’s perfectly fine to submit the same proposal for the same event again next year.
Wish you best of luck!