In his excellent 1945 essay "Politics and the English Language" George Orwell lays out six rules to writing clearly and with purpose. Every aspiring writer should be obliged to consider Orwell's excellent advice.
A scrupulous writer, in every sentence that he writes, will ask himself at least four questions, thus:
1. What am I trying to say?
2. What words will express it?
3. What image or idiom will make it clearer?
4. Is this image fresh enough to have an effect?
And he will probably ask himself two more:
1. Could I put it more shortly [i.e., concisely]?
2. Have I said anything that is avoidably ugly [e.g., wordy, extraneous]?
I have provides brackets to clarify Orwell's meaning, even as it may prove to be unnecessary, saying a sentence is "ugly" has, itself, become an outmoded colloquialism. Regardless, the outline Orwell provides is one which I try to adhere to each and every time I set pen to paper or begin to type on my keyboard. Those who fail to write clearly or fail to get their meaning across typically do so because they have failed to observer these six points.