^do not 'start and proceed' with DXM. Research about the different effects you get from the fourth (maybe five) plateaus, and take the dose according to that. 100mg will make you feel hyper and high but if you're not P450 2D6 deficient (chances are 9 in 10 you aren't) you won't get what you want. And in the case you are cytochrome deficient, you won't die from taking 300mg.
Well, you're asking a super indoor person, and that's obviously applies to psychedelics, even more if it's your first time on any psychedelic, and that applies even a little more if DXM could be your first psychedelic (how many times did I say psychedelic without counting the last one?)
On a second plateau dose, which I think you will get from 300mg, I like to get my room as dark as possible and watch the OEVs (yes, it's some kind of special OEVs, it's pretty cool depending on your set & setting, and since this is your first time.. yeah, you'll like it), while liying in my floor (yeah, floor, I don't know, I like to trip on DXM on my floor, a bed works too), and listen to tecno-melodical/rock music, I don't know your flavor. About 2 or 3 hours after the DXM intake I begin to close my eyes and get creative CEVs (btw, OEVs = open eye visuals, CEVS = closed eye visuals). I recommend trying that too. And you always can try to think about fixing your life, your social status, your "big problems", even your car. Sometimes DXM do wonders.