Take practice tests earlier and throughout the GMAT study process. I was discouraged early on with my performance on practice tests and thought the best approach was to spend as much of my time studying and doing OG programs as possible. I waited until a week before test day to take my first real CAT. I was totally rushed, got flustered by the whole process, and did terribly. I took me awhile to adjust to the CAT setting (eg, if you start doing well, your problems become consistently difficult with no respite). I ended up being rushed in both quant and verbal during my first time taking the GMAT and performing below expectations.

My second time through taking the GMAT I made sure to frequently take CATs throughout my study process. It not only improved my timing and test form (ability to withstand difficult problem after difficult problem without fatigue), but the metrics many of the CATs product allowed me to identify weaknesses. It also helped me to realize when I simply had to move on from a problem I didn't know and go to the next -- it was very difficult for me at first to "admit defeat" on a problem, but there is simply not enough time to work through something you don't know. Ultimately, the best way to do practice problems is through a CAT -- its the most realistic and useful type of practice problem one can do. So my best GMAT advice would be to take CATs early and often!