How to let go of the will to let go or reach a certain state? I find that the biggest block in my practice is the will to reach a good state. There's constantly an expectation from the experience to be good. I found that only by letting this go you can truly reach a good state, but its very hard to let this go. Countless sittings are wasted on this.

How can I learn to let go of this need?
Great question ,this is actually a fallacy that ,I myself experienced after reaching long periods of bliss during meditation .What you are experiencing is called rapture,you  started off well in meditation without expectation then when the blissful feeling came, instead of meditating on it, you became enchanted by it and thus wanted to have it back but you cant have it because you started desiring it,falling back in the loop of desire> attachment> suffering.

What I had realized on the experiential level,is that there is no where to go in meditation ,I am already there ,all what I need to experience ,I am already experiencing.I realized that each experience whatever it is can be an object of meditation , a door way to end suffering.....Now If I cannot reach a certain state then the reality is ,,that I cannot reach it :).. knowing that right know and meditating on this reality by itself solves the problem.The quality of not reaching you cannot accept, you have an attitude towards it.When you accept not reaching the state you will transcend this thought.Then the state will come out of no where,its a state of connection with existence. 

See the issue meditation is trying to solve is not to keep you in a spiritual high,but to make you less possessed by things as well as not making you disinterested in life.Thus if you totally accept life as it is ,with its bad states as well as its good then you have understood the way.

I recommend Vipassana meditation.Don't try in it to reach any state ,whatever you experience is your reality.No need to go anywhere or force any action.