The best advice I can give you- and this goes for every lesson in my class “Is to listen to as many native speakers as you can”. The more you listen to native speakers, the more comfortable you will become with what people say when they want to express a certain meaning.
As a logical as the rules in Spanish seem to be (and they may not seem very logical to you) learning a language is NOT like learning mathematics or the sciences. A language is an organic, breathing thing, is a God creation for human beings, so we need another human beings to associate... with lots of room for impreciseness, ambiguity, and imperfect grammar.
Once you become familiar with the building blocks in Spanish, you shouldn't have to think hard when you’re speaking. Rather, you should be able to listen to what others say and imitate their expressions – even without knowing precisely what it all means in English!
I’m native Spanish speaker and I want to help you!
God Bless You!