I've been here for ages, on and off. I like:
- Copy-editing for style. Less is more, terse beats flowery, euphemisms are bad, "In October of the following year..." --> "In October 1872..." Breathless prose is also bad. "Revealed". Elegant variation. Puffery, hagiography and fanspeak. We aim for a neutral encyclopedic tone here.
- Cliché. Duly, promptly, eventually, actually, simply. Adverbs (and adjectives) especially need to be used with care. Aforementioned. Notwithstanding. Unbeknownst. Subsequently. Additionally. In fact. Finally. Moreover. Individual, when used as a noun, to mean "person".
- "Not only... but also..." should be used very sparingly. "Not only was Jesus the son of God, but he could also do miracles."
- "A number of..." Zero, pi and negative nine are perfectly respectable numbers. Do you mean "several"? Even better, give the actual number if it's known. See also this comment. Nine!
- However, while, although. Use with great care; they may not mean what you think they mean. Don't write "but" when you mean "and".
- Reducing overlinking. It's such fun to insert these lovely blue links. But with them too, less is more. The right number of judiciously targeted links is more effective. We used to see a lot of New York City, New York, United States. Links two and three really do nothing but distract.
- Sourcing. This has got better over the years, but is probably still the number one flaw in Wikipedia. It's possible to insert some garbage about a minor artist or a major road sourced to a blog and have it remain there for years. We need to be more vigilant, for biographies of living people, but also in general.
- Colloquial language. "Up to Glasgow", "down to London". Not only tonally wrong, but if a word can be removed without altering the meaning an iota, that's a word that shouldn't be there.
I'm restricted in the time I can give to Wikipedia for various reasons, but if I can help you with anything, ping me on my talk page. I'm a serious and straightforward guy, and I'm not interested in communicating by edit summary. I try for a very short summary, and anything I need to say, I say to the right person in the right place, at the right time. Treating people with the respect they deserve is the only way to maintain a collegiate environment. Having had two teenage kids has really helped me in this regard.
The key thing in life is to check one's ego, don't sweat the little things, and be aware of what you're good at but also your blind spots and potential triggers. Few things are genuinely urgent, and nothing really matters all that much. At the end of the day, we all die, and the Universe itself is temporary.