You can also use a 24" dish instead of an 18" dish if your signal is a bit weak. This won't help if the problem is overgrown trees, but it can make a big difference during storms.
I had usually found that I could move the dish up/down/left/right about 1-2" and keep the signal, strength would obviously vary over that distance.
It's easier (IMO) to aim the dish with an on-line signal strength meter with you right at the dish. The meter will respond faster than the software on the STB, and it's easier to work with
