If you want to build your vocabulary, how do you decide which words to spend the time and effort on to really learn? While there are a hundreds of lists out there and everybody’s list has different words, my advice is to create your own list. Start noticing the words you keep seeing but don’t yet know well enough to use and write them down.
These are the words that will have the biggest pay-off if you learn them. You have already seen them in action so, even though you may not think so, you already have some idea of how they are used and what kinds of words they are. You will be more interested in finding out what they mean and how to use them because they are already in your world.
For now, just start making a list. If you aren’t sure how to spell a word, write down your best guess, put a question mark by it, and fix it when you come across it in print. If you are willing to do a little extra work, write down how the word was used (was it describing something? If so, what? Was it an action? By whom?) But just listing the word is enough for now. The act of writing it down will invite it into your brain. In step 2 (coming in a few days) you will start to claim it as your own.