Fly the correct speeds! These will almost certainly be lower than you think they ought to be.
Target threshold speed Vat = 1.3 x Vso i.e. 1.3 times stalling speed in approach config
If you're not sure about the aircraft's stalling speed at a particular weight you can always stall it at that weight - with an instructor if need be - then you have a reference point for calculating Vat
Then if the resulting figures are lower than you're used to flying the aircraft at, have a practice - again, with an instructor if need be - at flying the aircraft around at that speed to get the feel for it. That should make you feel comfortable that the 1.3 margin keeps the aircraft nicely in a controllable regime.
Same applies on take-off - if the flight manual best takeoff performance says rotate at X knots and climb at Y, then that's what you should do - adjusted for weight of course.
NS