You can start by capitalizing the first word in each sentence that you write.
Reading is absolutely the best way to build up your vocabulary. I'd say that whether English was your first or 23rd language.
You read in order to learn words and how they are used in context. When you encounter a word, you make a note to look it up later. Often you can figure out from context what it may mean. If you can't figure it out, then look it up right away.