Mix the powder in with 0.1 to 1 cc's of water (I find 0.1 cc is all you need). The powder should completely dissolve upon hitting the water (with the help of a little shaking). There is no need to cook the shot.
If you have a vial, the liquid was made to be im'ed. If you are talking about mainlining, I would definitely not advise that. I can promise you that you can get plenty ripped, and I mean RIPPED from snorting it. I remember the first time I went into a k-hole, it was unlike anything I ever tried.(Was experienced with LSD, Psylocybin, MDMA, AMT, ect.)
IVing K is a lot different than snorting it. It's only going to last roughly a half hour to 45 minutes when injected. After you're done with your shot, literally within 5 maybe 10 seconds after you pull it out, you're going to be facing (make sure you get the orange cap back on real quick before you start rushing and fall over with it in your hands). Some people have said that they can't get the needle out before they are in the K hole. I've always had a matter of a few seconds, but for others, it can be a very instantaneous thing.
If you IV ketamine, you're going to want to be around people because the first time you do this, more likely than not, it is going to be more intense than you'd like it to be. You don't want to black out by yourself. You don't want to black out with a stick in yourself.
Don't be inexperienced with psychedelics and then do ketamine. That's the most obvious one of all.
The reason why IV K is so enjoyable is that when you get the right dosage (one where you can still breathe comfortably and don't get nauseous as shit but you're still tripping hard), your whole body will go numb (won't be able to feel your tongue, teeth, face, etc...don't let it frighten you), you will become dissociated, so walking will be a challenge. Despite this, it is still possible to function if you pull yourself together. I was still able to help administer someone else's IV dose while beginning my first IV k-hole.
All in all, most people prefer snorting as they claim it is more pleasurable. When snorted, you have a while to enjoy the come up, whereas when IV'd, it hits you like a brick wall.
If you're inexperienced with the majority of psychedelics and are going to try K, snort SMALL amounts first, and be around a trusted friend. Trust me on that last part, you'll want to be able to have someone to talk to if it gets intense enough.
Finally, I will say, IVing ketamine is like IVing coke; if you do enough, you'll get one fucking hell of a bell ringer. This can be part of the addictive nature of both of these substances, and likewise, it can also freak people out to get a bell ringer from ketamine when they haven't tried nitrous or IV cocaine (or probably ether which I could see giving people bell ringers, but I haven't done ether before).