I will give you the simplest formula that I have been using over the years, that if you want to build your vocabulary or learn how to read or spell flawlessly or write effortlessly or speak intelligently, it all begins with keenest desire from the inside to want to improve on onself. Obviously, there is no how one give what he/she don't have. Same is application to knowledge acquisition. Apply yourself intently in whatever you want to be good at, and believe me, in no time you would start to see results.
First of all, you must know how to read, and engage in it frequently. And as you do this, with time you would be able to spell correctly, as you become conversant with the words as you read. Then you can start learning how to write since you must have been familiar with how sentences can be structured. Afterwards, the final practice would be learning how to articulate as you speak, as you strive to recollect everything you have been exposed to during the course of reading, spelling and writing. This is the surest formula you can adopt in building your vocabs.