Keep a log of every system change you make, including at least the date, if not also the time that you made the change.
For each log entry, record what you observed, and the reasoning that prompted you to make the change, as well as the steps you performed.
As you learn, you will find there are many small tweaks that you don't need to log; but you do need to record changes you make to the way the system operates. When in doubt, record it. Over time, you will refine your understanding of what to record.
If this seems like a pain in the neck, wait until you have done something, but you can't remember when or what; and now your system is behaving strangely, and you haven't the slightest idea how to begin to fix it. If you call in a tech, he's going to ask you what you did.
However, with a good record of your changes, a review of your System Event Log, and a rough idea of when the problem began, chances are very good that you can identify and fix the problem yourself. If you can't, then you'll at least have a meaningful answer for the tech. Generally, a quick solution will cost you less.
This is a Trade Secret because, although it is extremely valuable and easy to do, it is only practiced by the technically elite!
An Easy Change Log
Create a folder and name it "Change Log". In that folder, record each system change entry in a new file, using your favorite word processor or text editor.
Name the file "yyyymmdd title.txt", where "yyyymmdd" is the year, month, and day, and "title" is a short, meaningful phrase which will remind you, at a glance, of the contents. For example, a filename like
"20070623 Disabled MagicBuy due to high cost and spyware.txt"
is much more useful than
"Stopped Program.txt".
Including the date in the filename insures that your change records are nicely organized by date when you sort by filename. (Learn about creating and managing files and folders on our File Systems page.)
Error log
While you're at it, create another folder next to your Change Log, and name it "Error Log". Use the same method of naming your log files:
"20071007 WD 500GB USB Drive failed to connect.txt".
Record the exact text of any error message that you see. If the message refers to a known application, check its Help for a solution. If you know the manufacturer, go to their website and run a search for all or part of the message text, or your best description of the problem - chances are good that somebody has already solved it.
Caution: if you indescriminately "search the Internet" for a solution, you may encounter scams and you will find many more bad solutions than good ones.
When you resolve the issue, record your solution in your error log file, then rename it by adding "-Closed" to the filename:
"20071007 WD 500GB USB Drive failed to connect -Closed.txt",
then move the file into your Change Log folder. If the problem reappears after you've forgotten the details, you already have the solution at hand.
Inventory
As a useful variation of this scheme, you should make a list of your hardware and software, including brand name, model, serial number, and version where applicable. If you call a tech, he will want to know these things. So will you:
You see an ad for some new software; but it says it's not compatible with certain versions of other software or models of hardware. Your inventory can quickly tell you whether it's a good idea to install the new software, or whether you will need to upgrade or remove something else to make it work.
If you also include the name and location of the store where you bought it, and the date and amount of purchase, then you can quickly find where to return it and whether the warranty has expired, and you will have an inventory in case you need to make an insurance claim for personal property damaged or stolen.
If you also decide you'd like to store personal data - social security and bank account numbers, passwords, etc - in your inventory, then you really should encrypt the file so it cannot be read without a password.
Tip: Got too many passwords? Store them all in an encrypted file, so you only need to remember one to log on, and one to decrypt. AxCrypt is an excellent, free encryption tool.
In any case, remember to store a current copy of this inventory, and the means to decrypt it, in a separate, secure location.