There is a free online book called Inner Algebra provides ways and tricks to solve algebra in your head. This is extremely useful for student (and people who want to impress people). Methods include visualization, chunking, windowing , correspondence. Most of the techniques involve practice your mind to think on steps visually:
… There are a few key abilities that form a foundation for doing math intuitively. The first is visualization. It is similar to using your imagination. If you have always been a ‘visual’ person, you will find some things easier. The first part of this chapter helps you develop this ability. If you already feel skilled in this area, this section can help you strengthen it in the specific ways that help you use it for math. Some people are naturally quite good at visualizing. If you feel that you don’t really need training in this area, you can skip the first section. Just make sure you can do the exercises at the end of the chapter….
Inner Algebra – How To Do Algebra In Your Head – [Aaron Maxwell]