Check out SCAMPER
Scamper Creativity, Scamper Checklist – Mind Tools
OK, so the way it's written implies products, but you could just as well use it for fiction ideas!
Like the suggestions above, just write. I can't recommend highly enough the concept of just writing about anything for 15 minutes a day for unblocking. Writing is a discipline and even if you just write 'I can't think of anything to write' 500 times or your shopping list, it's ok. Eventually, something will emerge!
Or actually try 'journal jar' - that's great too. Just google "Journal Jar" and get loads of links. You don't have to download anything and make up jars if you don't want to - just pick a topic at random and start writing. i'm always amazed that the most unpromising-looking title will bring forth a couple of thousand words!