It's been a while since my last writing tip, and I just have been doing more editing lately, so I thought I'd toss one more out there.
Vary your sentences!
Okay, I'm just in a yelling mood. But to elaborate, when writing, you need to think about the feel and flow of your piece as a whole. This is a somewhat more advanced tip than the tips thus far on this blog (most of the others are just syntactical), but this is stylistic and is, therefore, subject to more interpretation. That is, it is somewhat subjective.
However, I can assure you that it is still a valid tip to keep in mind. When you are assembling your sentences, think about how they sound in relation to the surrounding sentences. Do they all have the same length? Do they all have the same basic structure? Do they all have the same pronouns repeatedly? Do you feel assaulted when reading them together?
Take the last paragraph (just before this one) as an example. I asked four questions in a row. Each of them has more or less the same structure and length, and had I asked just a few more, I imagine you would feel somewhat assaulted by the repetition. As it is, I was hoping to do two things: illustrate the effect you can get by using repetition and actually give you some meaningful questions to ask yourself.
It does illustrate that repetition, when used strategically, can be advantageous to not only get your point across but to do it in such a way that leaves the reader feeling a certain way about your text. Maybe you do want to assault the reader in classic tommy-gun style. But my guess is that most of the time you don't; you don't want to assault and therefore isolate your reader because then you lose rapport and they stop listening to what you are saying.
Repetition can also just be dulling. If you have the same sentence structure over and over again, your reader can become bored and lose interest. You don't want that, right? After all, what's the point of writing if you do it in such a way that readers lose interest and just ignore you?
So now for a fun example of repetition.
I got up. I walked my dog. I ate some breakfast. I took my daughter to school. I drove to work. I worked a lot. I came home. I ate dinner. I watched the TV. I went to sleep.
This is of course an extreme example, but we are all guilty of it to varying degrees. Now I will communicate the same information by varying my sentences.
This morning, I got up. I walked my dog and decided to eat some breakfast. After breakfast, I took my daughter to school, and then I drove to work. I worked a lot. Later in the day, I returned home, ate dinner, and watched some TV. And finally, at the end of this full day, I went to sleep.
As you can see (I hope), with a little work you can vary your sentences and make your text more interesting and appealing to your readers. You can do this by adding adverbs here and there, using dependent clauses, using coordinating conjunctions, eliminating pronoun repetition by combining actions by the same subject into one sentence, etc.
As an aside, note that I left "I worked a lot" alone. I did this intentionally to give an effect, to make the reader pause. The sentence is short and terse amidst longer more complex sentences, and it makes it stand out by stopping the general flow. You can do this when you want to draw attention to a particular thought.
I'm sure that I haven't done this subject justice, but I hope you will think about it more when writing if you don't already. And as you incorporate this tip into your writing, you can take it a step further and apply the same rules to paragraphs: vary your paragraphs! This means not using the same transitional phrases repeatedly, varying their length, etc.
Forget the "every paragraph must have three sentences" rule if you were taught it. It's garbage. The more important thing is that paragraphs communicate a complete thought, so if you can do that and add variation along with it, you're on the road to writing better!