If you want to read more Caesar to build up your vocabulary and overall reading skills, there's De Bello Civili. It's shorter than De Bello Gallico, but a bit more difficult, you'll probably find. If you'd like to read some easier Cicero, I'd suggest some of the relatively short moral/philosophical works like Somnium Scipionis (that's book 6 of De Re Publica, but pretty much a self-contained narrative. Very short and interesting.), De Senectute, or De Amicitia. Stay away from Ovid for now.
Reading is surely the safest way to build up your vocabulary. Look up all the new words you run into, and perhaps make a vocabulary list for each paragraph. Rehearse the list a bit, and read the paragraph 2-3 times to rehearse reading and seeing the words in use. It's a bit tedious, but it will help, and of course you don't have to go through the whole texts like that.