A lot has been said about this before, here for example, and elsewhere on this blog, for example here, however here are some more personal thoughts on the subject.
Think about what you want to do
Go for a walk somewhere nice and have a think about what you want to say, and especially – how are you going to say it, take your time – mull over your ideas until one of them just goes “click”
A talk is usually shorter than a workshop, and although a workshop should include more “audience participation” than a talk it’s nice to give everyone a chance to at least say hello to their neighbour.
Choose a subject you are PASSIONATE about!
Not only will you shine with enthusiasm during your presentation but as you are going to be working on this subject for a while (we all hope!) including when you practice (which you will !) and repeat yourself endlessly then it had better be something you believed in.
Don’t try and guess what will be the “in” subject
Even if you could predict the future would you choose a subject everyone will be talking about or avoid it for something more original?
I realise that this is a very personal opinion, but I really think that most teachers (and by that mean me!) would rather take away some new ideas to use in their classrooms than hear about some detailed research you have undertaken, unless of course there are some obviously useful tips teachers can integrate into their lessons.
Remember the buzz you get from stepping outside your comfort zone? This is really your chance to put yourself on the line, the best way to learn is to teach so giving a presentation is the ideal way of perfecting whatever you are going to talk about.
What advice would you add?