Choose two holes on the practice green that create contrasting conditions (uphill/downhill or sidehill). Putt back and forth ...
To see success with putting, distance control is everything. Sure, it helps to have the ability to read greens and to understand slopes, but when your speed is precise, you make a very difficult sport ...
When putting, many amateurs think that line is more important than distance control, but that is false. You can have a good line, but if you hit it 20 feet past the hole, it is a wasted effort.