I have a small suggestion...
When reading a work with difficult words, always keep a small dictionary beside you. Look up words immediately when you don't understand them.
It sounds tiresome, but it really helped me quite a bit when I was trying to expand my vocabulary. If it's a word you really wish to know, reread the definition a few times over, and practice with it throughout the week.
Just a small tip
As far as writing goes...
Write ALL THE TIME. Choose topics that are varied and sometimes difficult (a challenge is a good thing, those can compell you to improve quickly
). Look around, find a random object. Write a paragraph describing it. Take a drink, describe the taste. Touch the carpet, describe the texture. Etc etc.
Unusual descriptions really broaden the imagination... not because of the ideas, but also the word choice. You start to learn what word choice frustrates you, and what phrases you love.
But to make this work, make sure that you never remove sentences! When you're writing, just keep going, no matter how bad the work sounds. Keep writing and finish it until you have a decent amount of words on the paper. A HUGE aspect of improving writing (or anything similar) is to accept that sometimes it won't sound so good, but Practice Makes Perfect, so just keep going, no matter what.
If you want to take it a step further, rewrite a few of these works. Re-edit them several times over (don't be afraid to get advice from others also!) until you have the best product you can
Hope any of that helps ^_^