No, I am not recommending the Print Screen key to capture your screen :-). Though that is the best possible free tool available to capture the screen shots, it lacks the power and flexibility of controlling the capture and doing the task in a disciplined way.
Tip : Use ALT + Print Screen to capture the Active Windows exclusively. This avoids the problems in tweaking the additional desktop area that’s got captured instead of a single window.
Now lets see how we can capture the screen more effectively.
01. Download MWSnap, a free screen capture tool (the best as far as I know..) from here and install.
02. Select the profile you want to capture. e.g Window, Fixed Rectangle, Menu etc…on the left side navigational menu. As shown below…There is a cool ruler also available to measure the size of the screen or your capture.
03. You are done with your screen capture. When you try to save this capture, MWSnap provides you a good number of standard formats you can choose.
04. Additional Features to decorate your capture.: MWSnap provides some cool effects to decorate your screen captures. You can apply a shaded frame, simple frame or a button look for your screen capture.
As per my experience with many free and commercial screen capturing tools, I feel that MWSnap provides a rich set of features, all for free (Donate Mirek, the developer if you really like to appreciate him).