Twenty Things to Know and Do when editing Wikipedia

Know how to add bold, italic and other format from the editing bar
Use the cite button and autofill, and {{reflist}} in a footer, to create footnotes
Start new sections with the Talk page button, indent with colons, sign with ~~~~
Use your Sandbox for drafting, graduating to the Draft: namespace
Currently, new accounts cannot create new articles
You become autoconfirmed by doing a number of edits and waiting 72 hours
Copy-paste moves are deprecated: use the move button
Articles need a topic sentence, and at least one reference
Notability of the topic needs to be established, for example with three decent references
Give context in the lead section
Build up drafts with referenced sentences, then rewrite for flow
Use understated and neutral language, avoiding editorial comment
Expect to: re-order (moving refs); divide sentences; sort into sections
Establish a good "logical flow" and then tweak wording
Add incoming and outgoing wikilinks to articles
Carry out major edits in a series of smaller steps with good edit summaries
Add categories and images: you can see how this done in the sources of articles
Use repositories: Google Books, Internet Archive, Wikimedia Commons
Be civil, and concentrate on content rather than debating points (not Twitter)
Beware conflict of interest, and back off if you are too close to the topic