I usually like to lag and nail it within a cube of chalk twice in a row. If I have time, I will check if balls go past the side pocket and spend some time slow rolling near the rails to verify the table is level with minimal roll off. Sometimes you don't have time to check out a table so it's best to not rely on the table or conditions to be perfect. I will also check out the 3 rail route if there is time.
Systems give you an idea of what to look for when at the table. If you can get past the systems and just "see" the shot, your game will elevate, but it takes a lot of messing around to get to that point.