Hand on throttle unless trimming until safe altitude 
Leave gear on single down until no useable runway remaining 
Check Aircraft POH/AFM for flaps or gear retraction first 
Walk field first determining ruts, bumps, or other obstacles 
Determine abort point if not airborne 
The time to determine takeoff and low altitude emergency landing path and/or points is before the takeoff, preferably briefed again in the takeoff briefing in the runup area 
Once airplane is moving, keep it moving 
Differences between grass, wet grass, mud, snow, dirt, dry lakebeds, gravel, sand, and other surfaces.