Set the timer for 10 minutes and produce as many ideas and thoughts in that time, don't stop, don't edit and don't develop. Just keep going - important! edit later.
Force yourself to change direction - don't go down a rabbit hole trying to make something work, chasing a thought that doesn't quite fit can really stifle your creativity. If it's going to work, it will come but, give it time - see next tip!
Really take a break and do something else - go for a walk, make a coffee. Stepping away will help give you perspective when you return.
Can you say it, or can you draw it? Tell someone, sharing your ideas really helps give you clarity and another perspective. True it can be frustrating if when you share it they don't understand or take it in another direction. But you need this feedback. You don't have to use it!
Brian Eno and Peter Schmidt created Oblique Strategies – to help break deadlocks and help resolve a creative dilemma. We think it really works. It also helps you practice the above tips.