Well, I've never smoked it. I've only taken the brew >.>
One of the big differences is the length it lasts in you (though I'm sure they both can feel like hours, weeks, months, ect. depending on the person). Smoked it's anywhere from 30 min - 1 1/2 hours (from people I know here), and from my own experience drinking it can last anywhere from 3 - 7 hours. The after effects can go on for a long time. Drinking the brew can leave you with a nasty headache on your temples and down the center of your brain.
Tips on letting go... well, I guess my tip is just make sure to remind yourself as you're lifting off that all will be well! Another thing to keep in mind is that you're going to this place probably with an initial thought or reason, so keep that at a focus as it can really make a big difference depending on the person. Just some suggestions. I know it can be hard to tell yourself you'll be fine whilst all the stuff starts to happen to you though.
I'll give you an example of how I feel just as things start up:
This is how I feel just as I start to lift off (well sometimes anyways): My head starts to feel like it's gonna lift off my shoulders, familiar things start to feel/seem less familiar (like your bedroom would feel less like it was a place you lived in), colors have a sudden change (since you'll probably be doing this at night it wont matter so much), my body starts to feel cold, and my innards feel like they are an ice cold beverage. My body thereafter starts to feel like it's spanning and soon after it feels like I am breathing in fresh snowy mountain air and the air feels like it goes through my whole body and my body feels like its all breathing, and my body begins to feel like it's changing shape, stretching and dissolving into the air.
If you feel things like that, just remind yourself that it can be considered normal. If you feel like puking, hold off until you start to at least feel a noticeable change in the space around your body.
I think to some degree a shaman will help prepare you before you take that journey and he/she will be present with others while you go through the motions to make sure everything is going as it should.
Hope this offered some kind of explanation that may leave you with some comfort