- Always search if the bug hasn't been reported earlier
If you report it for second time, that will clutter developers' job and add unnecessary work for them. Usually there is a list of known bugs, reading it will make your life easier. If you have more helpful info than in already existing report, you can add it as a comment or reply.
- Make sure what you found is really a bug
People usually report things, which simply haven't been made yet. Such as missing text, incomplete descriptions, missing UI parts etc. You should not report such things, just skip them.
- Describe the problem detailed and very clear
More info is always better than less info. The more details you remember and write, the better.
- Everyone likes reproduceable bugs
If the bug doesn't happen every time, try to find ways to make it happen again. Generally speaking, your job as a bug hunter is to make that bug happen in developer's computer. If needed, write step by step instructions. Though if you can't reproduce the bug, your report may still be useful.
- One bug per thread
Every thread is for a single bug. Don't put several bugs into one post, that makes tracking difficult.