Do you know Object Oriented methodologies? If so (or if you want to learn), consider something like java or python. Are you coming from front end web? Learn node.js, it will have the most transferable knowledge.

Find the best, clearest tutorials that lead you to something similar to what you want to build, and use that tech. Personally, I'll use python/django for my next webapps because I like the tutorials and the programming style/environment. But I don't do games, and django probably isn't the best game framework.

I'd definately use HTML5 for the front end, I love the api's and the skillset is very valuable.