Before you are cleared for takeoff or take the runway for a departure have a plan. An escape plan. Should you have an emergency in the following phases of flight have and commit to your plan. Take into consideration, the conditions of the runway, is it day or night, are you current and proficient, is this your home base or not, where your emergency equipment is and how to use it. And use your passenger as a tool in an emergency, be sure to brief them. Two heads are better than one.
On the takeoff roll if for any reason you don't feel like you should continue - throttle to idle and apply breaks. Reasons may include the tachometer is not reflecting full power when you have full throttle in, Airspeed Indicator not showing that you are gaining speed, you notice a change in the windsock and should switch runways , etc.
0-500ft AGL if you had an engine failure - pitch for best glide and land straight ahead. The desire to turn around and land on the runway is strong but one you MUST overcome, it is best to land with the plane in control and walk away with maybe a ding on the plane and you than attempt to turn around and risk the very possible outcome that is less that favorable. If you get my drift.
500+ AGL if you had an engine failure - pitch for best glide and perhaps make a little turn left or right (still mostly ahead) See the above comment, Do you have time to follow the checklist?? You may have time to do the items you have memorized - that is something you have to decide while safely on the ground before it happens. Clearly the main objective is to be safe and walk away, if all you have time for is to pitch for best glide and land safely in a field then you did a great job!
And finally always be thinking through out your flight - what are my options for a good place to land should I have an engine failure.
NTSB report http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070627X00820&key=1