Okay, I'm going to explain Strafe Jumping for the people who aren't familiar with the method. This trick generally applies to ScoutsKnives only.. but can work on low gravity surf servers.
We've all seen the guy flying through the air at insane speeds, left and right making him nearly impossible to hit, this is how you do it.
First step: Go to options>keyboard>advance> and check the box that say developer's console. Close options
Step 2: Hit ` , and in the box, type bind mwheeldown +jump This will bind your mouse wheel to Jump. Hit enter, and then type cl_yawspeed 300. This will make you turn faster in the air, optional.
Step 3: Join the server of your choice. You're jump is now binded to moving the mouse wheel down. Jump through the air, and once you're in the air, you won't hit W again, not even when you land.
To go left, hold A and move your mouse to the left, to go right, Hold D and move mouse to the right.
Step 4: This is the most important part..
Right before you land, begin rolling your mouse wheel down.. and continue rolling it as you hit the ground. You'll instantly jump again, and continue your flight. You'll gain speed as you continue to do it smoothly.
Further tips: Do not fly in straight paths, or predicatble ones. AS it will make you easier to hit. Do not overuse this, still take time to stop and shoot.