THE FOLLOWING IS A SIMPLE METHOD PRACTICED BY LOCAL PILOTS 

1) Lean to peak RPM  or

 2) Set the fuel pressure/flow to the figure recommended by the engine manufacturer for the Density altitude.

 Both of these I find work out about the same and the second one is probably the simpler.

THE FOLLOWING NOTES ARE AS SUGGESTED BY THOMAS TURNER OF THE AMERICAN BONANZA SOCIETY

The absolute, best way to find maximum horsepower for takeoff is to go to full throttle/full rpm on the ground, lean to about ~75F/40C* rich of peak EGT, release brakes and go.  The reality is that puts a lot of strain on the airplane you might want to avoid.

 Instead, try this:  Before your trip, level off at a fairly low altitude and go to full power/full rpm.  Lean to find 75F/40C rich of peak EGT and look at the EGT (for any given cylinder; most people use the hottest).  This gives you a target EGT for maximum horsepower for takeoff pretty much regardless of altitude.  Now when you depart a high elevation airport, come to full throttle/full rpm and quickly lean to get the target EGT plus or minus a few degrees.

 Other technique:

• Hold the brakes at the beginning of your power-up for takeoff until you have power and mixture set.  A "rolling" takeoff will use significantly more runway, especially at higher elevations.
• Do not use flaps for takeoff at high elevation airports.  They will generally increase your takeoff distance at high density altitudes, and significantly reduce your initial climb rate.
• Don't "rotate" or pull the airplane into the air.  Add back pressure and let the airplane fly off when it's ready.  The mishap record is littered with reports of airplanes that were horsed into ground effect when taking off from high elevation airports, only to be unable to climb out of ground effect before either settling back into the ground or colliding with an obstacle off the end of the runway.
• Limit the pitch attitude after takeoff until the airplane accelerates to Vy speed or better.  With less thrust available at high elevations it will take only about 3 to 5 degrees up on the attitude indicator.  A higher pitch attitude increases drag and invites a "mush" back into the ground.
• Don't be in a hurry to retract the landing gear.  The inner gear door increases drag, and the moving landing gear induces angle of attack changes that add drag and reduce performance.  Also, you want the wheels down in case the airplane settles back toward the runway before finally climbing out.