Here be some Selenium guidelines (mostly for writing, but include running here too).

IDE

click vs. clickAndWait - use the latter on anything that requires network activity, but if you use the former on other buttons/links, your script will pause indefinitely
verifyLocation - use w/regexp; otherwise it'll be absolute (I think)
- e.g. ...
wherever possible, use relative--not absolute--URLs in |open| commands

PHP

Locating elements
- xpath: for elements that have dynamically generated xpaths use 'contains'.

         for e.g. if xpath for 'remove add-on' link has the add-on ID 
         in it (id('addon-2464')/a[1]) and we do not know the add-on ID then
         we can write the xpath with 'contains'
         //div[@id,'addon-2464'][2]/a[1]) => //div[contains(@id,'addon- ')][2]/a[1]

- If you want to match on the text in an element

//a[text()=’My Text’]: matches a link whose text is “My Text”

- If you want to match more than one string in attribute or text

//a[contains(text(),’Bill’) && contains(text(), ‘Clinton’)]: matches a link whose text contains both Bill and Clinton. You can use any xpath function or operator to create your expression

- Find the nth element of a type

//div[position()=3]: matches the third div on the page //div[@id=’abc’]//table[position()=3]: matches the third table inside the div whose id is abc

QA/Execution/Web Testing/Selenium Guidelines

IDE

PHP