Beginning writers are especially prone to flowery language, meandering sentences, and too many words conveying too little information. One can attack wordiness by eliminating redundancies, deflating inflated phrases into concise ones, and simplifying needlessly complex structures. Passive, rather than active, voice. The goal here is to write vigorous, direct sentences rather than flabby, indirect ones. Avoid passive voice.
Active voice is less wordy, more direct, and often clearer.
This is a more subtle point that when mastered brings one's writing clearly up a notch. Shifting to wrong tenses. When writing history, it is almost always preferable to use the past tense. Misplaced or dangling modifiers. An infinitive is to and a verb.