One important thing in blender is its interface. The golden Rule for this interface is:
Use the shortcuts (keystrokes) because they save you very very much time and allow precision modeling!
For sure you will need some time to remember them, but you will be incredibly fast after a while, if you learn them from the beginning! Here i will post some of the common and usefull shortcuts. This list will be expanded soon. The most usefull shortcuts are on the top of this list.
First time when you use blender you will have a feeling common to the "lost in cyberspace", its like "OMG too much stuff here, too complex, i want to close it!" But after a while you will see that its interface is very good and well planned.
I suggest to NOT make anything if you didnt read a basic tutorial for blender. There is almost no chance that you are understanding blender by "just trying around". You will get frustrated with this and think "Blender must be crap!".
But if you do some tutorials you will see how genius it really is!
Oke enough explained. Here are the keystrokes:
Some of these Keystrokes work only in Edit mode, some of them work only in Object Mode.
If not marked it will work in any mode. Most of these shortcuts only work if you point your mouse inside the 3D window.
(EM) = Edit Mode
(OM) = Object Mode
(LMB) = Left Mousebutton
(MMB) = Middle mouse button
(RMB) = ... I forgot it
"Shift" + "RMB" Multiselect
"A" - Select/Unselect all
"Ctrl" + "J" Join Objects (OM)
"Selected Faces/Verts/Edges" + "P" - Seperate from Object (Creates a new object with the selection) (EM)
These commands need to be applied with Return to close "Command mode" and apply the changes.
If you decide to not change your Object you can abort with "RMB".
"S" - Scale
"SX" - Scale on X axis (apply with "Return" or LMB)
"SY.5" - Scale Y axis to half size
"SY2"- Scale Y axis to double size
"S" then "Shift" + "Z" - Scale all axis but NOT Z (Works with other axis too

)
"RX45" - Rotate X axis 45degree
"M2" - Move Selection to layer 2 (OM)
"Shift" + "D" - Duplicate selection (Press "RMB" to not move the object with mouse)
"Num0" Camera view
"Num1" Side (Y) view
"Num7" Top (Z) view
"Num3" Side (X) view
"Num2 4 6 and 8" Rotate view Down, Left, Right, Up
"Ctrl" + "Num+" - Increase selection of Faces/Verts or Edges (EM)
"Ctrl" + "Num-" - Decrease selection of Faces/Verts or Edges (EM)
"Ctrl" + "U" Save actual Scene/Materials and Textures to User Default. (Everytime you start a new scene it will look like your save)
My Blender Tutorials for Beginners (german): http://www.youtube.com/user/voxelgeek