change your mindset
Keep in mind not to overrate grammaticality. You should only care about grammar as much as you need to be able to communicate your message effectively. Be an innovator! make up new words! Play with grammar!
Of course, don't be afraid to make mistakes. I encourage mistakes because nothing makes things quite so learnable. I do understand that this is easier said than done.
read more, read anything
Sometimes I am able to articulate my thoughts well but other times I just mix up things confusing myself and everyone else.
I've been there! Sometimes it seems like your tongue just does what it's supposed to do, and other times, it's tied to a railroad track. The best thing you can do is read. It seems counterintuitive, but the more you read, the more your tongue just does what it's supposed to.
Linguist Stephen Krashen and others stress this. Read anything in your target language. And read a lot of it. You should strive to be that guy who's read the most in the room, or in the school, or on the planet.
You will not learn new ways to express yourself by speaking. You must do that by understanding others. That being said, however...
In the car, on the bus, walking to class, wherever—make sounds in your language. If you think pronunciation is getting in your way, try listening carefully to some recordings. Practice those sounds like a child practices sounds, if you're brave enough!
If you're the studious type, learn the IPA. Study phonetics and phonology. If you have trouble figuring out what sounds a speaker is actually making this will help a lot. Be forewarned, it does take a bit of time investment to learn this.