3 day TBT is fine.
5 day split is also fine.
It's basically horses for courses.
The main don't are.
1. Never lift more than you can handle. if it's a new exercise or one you haven't done for a while, BE CONSERVATIVE. You can always a add a little more weight onto each set, until at some point you find the "happy medium".
2. Don't use exercises like behind the Neck Press, Lat pull-downs, behind the Neck, pull-ups behind the Neck, as you cna potentially causes rotator cuff injuries.
3. Don't waste time on things like wrist curls, you might damage the joints. The same could be said of things like Wrist and Ankle weights. You're just putting stress on small joints.
1. Always lift equally on both sides of the body. I.E. Cable crossovers where the hands meet in the middle, not where one Arm ends up infront of the other and when doing one armed or legged exercices, use the same range of motion, rep speed and number of reps on both sides.
2. Make sure you keep the range of motion quality, as too often people start out good with it, then slip into a sloppy way of doing things, I.E. Pressdowns with a bent back and hunched shoulders, not a straight back and spine. People can get too comfortable doing something fairly regularly and lose proper focus on it.
3. Try to remember to breathe on every rep. When your heart is thumping after Squats it's a reminder, but it's easily done, because you're focusing so much on the technique.