I'd echo the advice given above, except that if you're using Gnome, definitely remove the hidden ".gconf" folder in your home directory before upgrading. Presumably, Gnome's configuration files aren't really backwards compatible, and from what I've seen, about half of the problems that users have complained about after having updated Mint (with the same /home partition) stems from .gconf, e.g. broken gnome-panel, broken app functionality (some apps store config files within gconf), etc. In fact, I'd delete most of my hidden folders before upgrading (I do keep some like .mozilla, for example, as I don't want to have to recreate my Firefox profile).
Another common mistake: if you have a / and a /home partition, make sure both are mounted with their respective mountpoints during the installation of a newer Mint release. I've seen plenty of people mount / but forget about /home...thus, they end up with a / partition containing /home, and a separate partition (the old /home partition). It's not too hard to fix though, with a bit of fstab tweaking.
Debian Testing x64/LM9 Main x64/Windows 7 x64 - LG R580 laptop w/ Intel Core 2 Duo T6500 2.1 GHz, 4 GB DDR2 RAM, Nvidia Geforce G 105M, Ralink rt2860 802.11n, 300 GB WD HD 5400 rpm