Updated: October 7, 2013
Steam is a highly popular, highly practical gaming platform, developed by the Valve corporation. The platform is quite flexible. Install and reinstall as much as you want, no silly restrictions, extra downloadable content and updates. You can easily replicate your games between multiple machines, and it comes with a decent two-way authentication security. It's even available for Linux, which is a really good thing. For you, as the end user.
However, like all software, Steam can sometimes go ballistic on its unsuspecting users. Things may go wonky or flaky or dodgy, and you will be left wondering how you can go about troubleshooting the issues without having to apply a hammer to your screen, or delete everything. This tutorial should help you resolve problems in a peaceful manner. Most of the stuff applies to Windows users, but still.
New game installs, first launch
Normally, you can run the Steam client without administrative privileges, and everything will be fine. However, some games occasionally need to write a bit of data to registry, which means you need these privileges. Indeed, in order to avoid semi-botched installations, weird errors with CD keys and missing configurations on a first launch of a new game, you might want to consider powering up Steam as administrator. Then, later on, you can continue playing as a normal user.
Now and then, you may find one of your downloads to have been suspended. It just reads, suspended, and trying to resume it will not really do anything. This is a fairly annoying glitch, and it does not have any simple answer. However, there are a few fairly bulletproof checks you could try to get rid of this issue. Let's see, starting with the least intrusive ones first. And remember, make all the changes while the client is closed.
Read-only option on game folder
You might need to change the game folder permissions for the specific game featuring that suspended download thingie. Go into your Steam top directory > steamapps > common, and find the correct title. Right-click on the folder, select properties. Then, on the General tab, uncheck the Read-only attribute, and apply for all sub-folders and files. Start Steam, see if this helps.
Delete download data
If the above option does not work, you might want to delete the download data. Again, in your Steam directory, go to steamapps > downloads. You will notice several .patch files and maybe directories listed in there, as well as orphaned directories without any associated .patch files, which most likely points at the problem you might be facing. Indeed, recently I had this issue with Red Orchestra 2, and the fact this game used to be a three-day trial back then did not help with the updates gone wrong. The contents of the folder shown in the screenshot below are indeed the game files. Try deleting these, or moving them somewhere else. Start Steam.
Steam does not start, connect or else
If this happens, for whatever reason, you are facing a somewhat difficult choice. You might want to try some rigorous deleting of various files. Steam keeps some of its configurations in two so-called blob files. You may want to rename them, or copy them to some other location, to see if this can help Steam recover from its glitches and start clean. I strong suggest keeping backups until you are certain that your problems have been resolved. The two files in question are:
Do note that this does not guarantee success. Moreover, you could be having a million other, unrelated problems, like your firewall, anti-virus, network and router setup, and more. But I won't go there. It is absolutely frustrating searching for help and getting random suggestions by random people that you do this or that, when you clearly know that the problem lies elsewhere. Especially if it used to work for you in the PAST. Therefore, I will not be suggesting anything of that sort. If Steam did what it should have once, then any future error will almost entirely be the client's fault, and the resolution lies there.
Steam does not clean old, orphaned downloads
You may also find leftovers in your download section, even after you have deleted the game's local content. This will surely annoy you. The two ways to resolve the problem is by restarting Steam or by deleting the ClientRegistry.blob file, which we saw just earlier, and restarting the client.
Last resort - be careful!
An even more stringent option is to delete the game contents and redownload them. For example, this may be necessary to resolve the suspended download issue. The next step is to purge the entire Steam folder, but this might not be feasible for most people, as Steam can easily contain tens or even hundreds of GB worth of game data. Backups are always useful.
Flash related problems on Linux
Keep your important game files backed up, in case you need to restore them. Allow Steam to finish its downloads and updates before closing the client. Avoiding interruptions will lessen the chance of weird bugs showing up and bleeding your time.
Some more useful tips and tricks for you:
How to install the official version of Steam through Ubuntu Software Center
Steam on Linux Mint; add the official repository and have fun
There you go. This tutorial may be completely useless to some of you, then again, it might save you a few minutes or hours of your time. Troubleshooting problems with any software can be tricky, because pretty much any case is unique. I tried my best to present the most universal picture I could. Either way, you do gain a wealth of useful data, like where Steam keeps its important files, game data, and downloads, about file and folder attributes, running as administrator, and a torrent of information on Linux and friends.
If you have other problems and possible fixes, I'd love to hear.