Big thing that I wasn't doing for a long time was really practicing. Anyone can go through some tactics puzzles for an hour, but really focusing and really committing them to memory is what will actually make you better. Calculation speed is sorta counter-intuitive I've found, the longer you spend on your calculations NOW, the quicker they'll be later. Until you get old and miss everything.
Cheers!
I just want to say that it is wrong to think that speed of thinking can be improved by solving tactics or other study.
Speed is real thing. It can be really not synapses speed but amount of neurons that lead to high speed. I have solved a lot of tactics but still very slow and cannot improve it no matter how hard i work. I cannot solve more than 22(usually less) tactics in 3 minutes although i solved 47 in survival mode. In chess speed is very important.