In a 1956 letter from C. S. Lewis to a woman named Joan Lancaster who had written Lewis soliciting advice regarding a piece she had written, Lewis lists five tips for 'what really matters' in effective writing (Collected Letters, 3:766). Great advice for us students.
1. Always try to use the language so as to make quite clear what you mean and make sure your sentence couldn't mean anything else.
2. Always prefer the plain direct word to the long, vague one. Don't implement promises, keep them.
3. Never use abstract nouns when concrete ones will do. If you mean 'more people died' don't say 'mortality rose.'
4. Don't use adjectives which merely tell us how you want us to feel about the thing you are describing. I mean, instead of telling us a thing was 'terrible,' describe it so that we'll be terrified. Don't say it was 'delightful': make us say 'delightful' when we've read the description. You see, all those words (horrifying, wonderful, hideous, exquisite) are only like saying to your readers 'Please will you do my job for me.'
5. Don't use words too big for the subject. Don't say 'infinitely' when you mean 'very': otherwise you'll have no word left when you want to talk about something really infinite.
One of the joys of reading Lewis is that he follows his own advice.