I like to start with the water/washer fluid first. Find a vacuum line on or near the Throttle Body that will feed all the cylinders evenly. Make sure it is not only connected to 1 intake runner or offset on the intake manifold so it would only feed some of the cylinders. If that is your only option you need to find an equal port on the other side of the manifold.
You don't want the line to be too big. If it is too big you can get a small vacuum line and usually shove it into the bigger line and it will seal good enough for what we need. 1/4" line is a good size, slightly bigger or smaller is fine as well.
Now start the engine and drive it around to get it nice and hot. When you get back connect the vacuum line to the port you found earlier and stick it into the gallon of water. You will have to give the engine a lot of gas to keep it running but just let it keep sucking it down. I usually run the whole gallon through the car in 2 or 3 treatments, broken up by me beating the heck out of it before coming back for the next one.
After you finish the water go drive the car hard to clean it out.
Now time for the seafoam, this is like the water except you need to let the car sit between treatments. Just like the water hook up the vacuum line and get ready to rev the motor up to keep it running. Stick the line into the can of seafoam and try to keep the motor running till it sucks up about half the can for the first treatment. Then let it bog out and die. Now let it sit for half an hour or so. Longer is better, for the first few treatments though you don't really want to let the motor get all the way cold.
Now go out and restart the car, it will take a little bit to restart, put the gas to the floor while trying to start it tends to help. Once started you should have one heck of a smoke show. The more smoke, the dirtier the engine is. You can let it idle for a little bit and have fun revving it so you smoke out the neighborhood or go for a drive and leave long trails of smoke. At some point go out and flog the car before the next treatment.
Now repeat the earlier process except use about 1/3 of a bottle at a time from now on so it lasts longer. Keep doing this a few times, you will start to notice that you have less and less smoke the more treatments you do. It will get to a point where the amount of smoke stops improving, thats when it is about as clean as it will get right now.
I generally will do one last treatment at this point, heavier this time. I will then let it sit overnight.
Dump any left over seafoam or marvel mystery oil into the gas tank.
The next morning start it up and go for a nice long drive, get the oil up to temp and keep it there for a good 10-15 mins if possible to help clean the last of the junk out of the motor. Could go to work and do it when you get home or whatever. Just don't put that many miles on it before changing the oil.
Now change the oil, and make SURE you change the oil, after all of this you will have some water and seafoam in the oil for sure, it needs to be changed. Refill the oil check all the fluids and there you go. It should now run noticeably better.
I have had GREAT luck with this regime on all of my cars but you do this at your own risk!