You can gain insight into your thoughts only with a lot of effort and patience. The actual process of gaining insight into thoughts is the same as gaining insight into emotions and body.
Looking At Thoughts
As usual you start with concentration and tranquility while working on insight into thoughts.
Start with looking at your thoughts, but don't get attached to them. Watch them arise and pass with calm objective attention. You can give your emotion a nudge in case it refuses to go.
And if it still refuses to nudge stare at it in the way you stared at your emotions. Consider it a set of pictures or words that the mind has created out of nothing.
Labeling helps with insight because it allows you to see the patterns that your thoughts follow. Use labels only for emotional terms like challenging, exciting, frightening and terms like hoping, memory and regretting. Look at the pattern of thoughts, whether they are positive ones or negative ones.
Patterns Of Thinking
Pattern of thinking throws an insight into your own nature and tells you a great deal about yourself. Just note insight if it occurs during meditation and start exploring it (what it is trying to tell you about your future) only after meditation.
Causes of Thoughts
If you want to go deeper, you need to know the reasons for the occurrence of the thoughts, their depth and what sets them off. When you see thoughts that give rise to these feelings, just observe what parts of yourself are you looking at.
Don't look through a set of different possibilities to find an appropriate answer. The answers should not be expressed but should be felt. The answers maybe in the form of impressions, pictures and symbols. Once you have an answer, see whether it still works in your next session of meditation or your real life. There will be other deeper revelations to come, so do not consider this a permanent answer.
Thoughts will lose their entry to awareness as you progress in meditation. There maybe periods where no thinking is involved, during this period feel the energy of unformed thoughts trying to break through awareness, but with failure. Investigate this energy when it happens.