Simple recommendations for good editing practice
Creating new articles: Avoid duplicate articles
Any given subject should be covered in one article: Camera wiki readers will be confused if there are two (or more) articles devoted to the Minolta ZZ-XYZ (imaginary example).
If you're thinking of writing a new article, first use the "search" option on the left of the screen to find out whether the camera or other topic is already described elsewhere. Remember that some cameras may have different names in different markets (e.g. one name for the Japanese market, one for north America, and one for the rest of the world). Also try the name with arabic numerals instead of roman numerals ("3" instead of "III"), with or without likely hyphens ("III-a" as well as "IIIa"), etc.
If you find that your subject already has a article, edit that article. If you sincerely believe that the existing article is an unsalvagable mess, scrap it and restart it (but use the article's talk page to announce this radical edit).
What's likely is that when searching within the wiki for information on the Minolta ZZ-XYZ, you'll find a general article about the entire ZZ series that devotes a paragraph or two to the ZZ-XYZ. You now have a choice: Either (i) edit the article about the ZZ series so that it says a lot more about the ZZ-XYZ, or (ii) create a separate article about the ZZ-XYZ. Consider doing the former unless the addition would throw the whole article off balance. Do the latter if you have a lot to say or if there's some other compelling reason. If you do the latter, feel free to reduce the discussion of the ZZ-XYZ that's within the article on the ZZ series, and make sure that you create links to and from the article on the ZZ series.
What we don't want is a situation where for a given, clear subject (e.g. a particular camera), there's some information in article A and not in article B, and other information in article B and not in article A — let alone worse messes involving three or more articles.
Changing existing pages: Value the work of others
Rewrite in order to correct factual mistakes, in order to make the result more readable, etc. If you're sure that a page is poor, salvage as much as possible of its informative content when you do the rewrite. Don't rewrite merely in order to make the result accord with your personal taste: a wiki is a group project. (As a minor example, if an article uses British spelling but you prefer American — or vice versa — leave the spelling as it is.)
Try to retain the images inserted by others: don't replace any image just because you have one of your own. Consider adding your image to supplement rather than to replace. However, there's no point in duplication, and if you're sure that your image presents all the information in an existing image and more information besides, go ahead and replace. If you have any doubt, start by linking to it and asking about it on the article's talk page.
Images in an encyclopedia are part of its information. The images for an enyclopedia about cameras should show, but if you can achieve this in some artistic way, go ahead. Just make sure that the photographs are sharp and informative where it matters. If you are thinking of replacing somebody else's photograph with your own, consider your own photograph at least as critically as the photograph that you might remove.
Respect established formatting
Wild flights of "creative" page design may be suitable in your personal blog; but camera-wiki.org needs simple, consistent article formatting. This will avoid confusing visitors, and helps present information in a professional and credible manner.
Before beginning a new article, look at the structure of existing pages—particularly some of the longer ones. For example, when laying out articles, use the standard headings "Notes" and "Links"; only capitalize the first letter (and proper names) in page titles, captions, and headers; do not use excessively large or tiny images; and avoid tricky markup (boxed sidebars, multiple columns, etc.) unless it is absolutely indispensable to your purpose. Remember that your page must remain editable by later contributors who may have no background in fancy markup techniques. Naturally you should always double-check your work for errors in spelling, grammar, punctuation, and so on.
If you are in doubt about the best practice in a particular situation (and there is no specific guidance in our markup reference or other help pages), it is generally preferable to follow the style guide at Wikipedia. The standards suggested there have evolved through much discussion, and will also be the established wiki format which visitors here will be most familiar with.
Provide an edit summary
It is considered good practice to provide a summary for every edit, especially when reverting (undoing) the actions of other editors or deleting existing text; otherwise, people may question your motives for the edit.
When other contributors scan our recent edits, an accurate summary helps them understand what changed and decide whether a particular edit should be reviewed or modified. When a major edit (e.g. deletion of a substantial amount of text) doesn't have an edit summary, there are fewer reasons to assume good faith and busy editors may be more inclined to revert the change without checking it in detail. Summaries are less important for minor changes (which means generally unchallengeable changes such as spelling or grammar corrections), but a brief note like "fixed spelling" is helpful even then.