Make sure you know what you're doing with salvia, a lot of people waste it by not doing it right. It's not dangerous physically, but a lot of people can be unprepared psychologically if they do break through.
I'd advise you not to do it after drinking, not because it's dangerous in any way, but because alcohol acts against most hallucinogenics. You wont get as good an experience as possible if you drink beforehand.
First of it's essential you smoke it in a bong. A turbo lighter is useful, but not essential. Make sure you get a big hit and hold for as long as possible. If you're vision starts to shake, prepare for the most intense and bizarre 10 minutes of you're life, not that you'll be able to tell how long it's been.
I've done Salvia several times and find it works best somewhere comfortable by yourself. My best experiences have been when I'm outside, especially if it's fairly dark.
As always, research on Erowid is highly advised:
http://www.erowid.org/plants/salvia/salvia.shtml
On the DXM discussion, the best method of ingestion in my experience is by bombing pure powder. Having said this, it is essential you have some accurate scales and know your dose and what sort of experience you want. I accidently overdid it recently and had a rather harrowing weekend.