When you're taking practice tests, I would suggest waking up at the time you'd be taking the real test. I took a bunch of mine at night and kicked ass, but I'm way more alert at night. When I took one in the morning, my score fell 8 points from the previous diag.
Also, when you wake up to take the diag, do a couple practice questions (like LR) to warm up your brain. I noticed that my first section when I took the test in the morning was always my weakest, so I tried warming up with 2 LR questions and by explaining 2 questions to my friend, and then the problem went away.
On the morning of the real test, I woke up at 9:30ish, and was leaving at 11am for the test. During that hour and a half, I did a games section that I had on my first diag and did a couple LR questions, then I got to the test site about an hour early, so I sat in my car and did some more LR questions, untimed. In retrospect, I should have done one or two reading passages instead/in addition, because the first section was reading comp, and I hadn't done a timed one for several days. Everyone else seems to agree that it was the hardest section, but I feel like I could have helped the situation by doing a passage while I was waiting for the test to start.
About courses, I took TestMasters, and I loved them.