Another vital way to look at sentence structure is to look at the diagram of the sentence. Now, I'm pretty sure no one diagrams sentences any more or (for our older readers) even remembers doing so with fondness. However, by looking at how sentences are built, we can examine how the reader's brain will process them.
For example, if you only have sentences that are Subject + Verb + Object, and they follow each other in basically the same format within the same paragraph, this will also thud. Vary the clause inclusions, the use of gerunds and so forth. Instead of "the monkey bit the dog." Try "After the dog stole his banana, the monkey bit the dog." Or "Instead of running away, the monkey bit the dog." And so forth.
Be careful with beginning sentences with gerunds though, as some structures are improper and can lead to confusion. For example, "Taking off my coat, I ate a sandwich". In this example, it is unlikely that someone would be taking off their coat and eating a sandwich at the same time. Instead this sentence should be structured as: "After taking off my coat, I ate a sandwich." This shows the sequence of events more clearly.
Remember to always think of your sentences in the context of the whole as well. Read your novel out loud to get a sense of how the sentences string together. This will also tune your inner ear to hear the inconsistencies and issues within the pages and paragraphs.