1. Plan ahead carefully (as best as possible). Examples: get a 7.1 Receiver/PrePro even if you now think you're never going to use it and/or that 5.1 piece price is very enticing. Pay attention to all those crazy audio/video standards.
Buy a Blu RayDVD player that can also play SACD.

2. Try and match components in terms of power/quality; if funds are not available at once, it's worth waiting, even though buying all at once may be exciting. Don't "cheap-out" on components, wires, plugs etc; plugging your M80's into a cheap Receiver will leave you underwhelmed and always feeling that something is missing.

3. Keep music in mind; in my experience, I've rarely seen a HT system used 100% for movies only.
M80 v3, 2 x Emotiva UPA-1 Monoblocks, XPA-5, UMC-1 PrePro
Pro-Ject RPM Genie, Carver C2 Phono Preamp