You have downloaded a mod and now you want to install it maybe this can assist you.

The very first thing you do with any mod or alteration to your site is backup all files that will be in anyway (manual or auto) modified either by the install scripts or by your following instructions.
The second thing is to ensure that you have a backup of your database. The database backup can easily be done useing the O-R Database utilitys in the admin area of your site.
The above instructions should never be forgotten allthough the install instructions on a mod may not stipulate them.

Ok we have the mod we have complete backups.
Before starting it is sugested at least by me that modules be tested first in a standard development to ensure that you can in fact get it working. While not in any way a requirement it beats haveing to replace it all later if you go wrong or the mod fails.
In most cases this would require that you alter your template setting to a standard template but if your site is allready heavily modified it pays to have a standard setup handy either on a home server or just a second folder on your site with different prefixes.

ALL mods come with instructions on installation and the creators include them for a good reason. No-one wants your site to crash and the mods are tested to install on a standard installation following the provided instructions. So in general if you follow the instructions correctly you should have no problems. If you do the best place to get instant help or at least fast help is by posting in the mods thread. Most mod owners would watch their own threads for replys (i know i do). So when you post they are notified and can resond as soon as they are able.

Note: While the instructions above are very basic it should be noted that 90% of mod install problems are from a simple failure to do the above before dureing and after installation.