As I've mentioned before, many of us write very well indeed with little or no knowledge about how our language is put together. Others of us are curious and want the additional flexibility that real knowledge can bring.
I've been thinking about an exercise that I often do with writing improvement classes I teach. I ask the students to pick one reasonably long sentence from their work (3-4 lines of type) and then write three more versions of the same information. Of course, it's helpful if they know the following information:
English has only four types of sentences although we can generate an infinite number of sentences within those types.
Simple: One independent clause (subject + verb)
Jack bought a new car.
Compound: Two independent clauses (subject + verb + coordinating conjunction (and, or, for, so, but, then) + subject + verb
Jack bought a new car, but his wife didn't like it.
Complex: One independent clause plus one or more dependent clauses
Jack bought a new car although his wife didn't like it.**
Compound/complex: Two or more independent clauses plus one or more dependent clauses
Jack bought a new car although she didn't like it and she told him so.
Once you've mastered these forms and practiced them a bunch (we are all using them all the time), your writing can really open up.