A good solvent weld begins with a properly cut pipe, doesn't really matter how you achieve the cut, could be by a ratchet style cutter, hand saw, chop saw, whatever, the important thing is that the end of the pipe is cut as squarely as possible. This will help provide the maximum bonding area inside the fitting.
After cutting the pipe, "deburring" is the next step. This means removing all the loose pieces of PVC left from the cut. I usually use a razor knife to do this but sandpaper will work or an actual "deburring" tool is available.
Next is "beveling", it's recommended that the end of the pipe be beveled 10*-15* to help entry into the fitting. Additionally this will help the glue from being wiped of as the pipe is being inserted into the fitting.
Test fitting the joint "dry" (without glue) is a good idea as well, your pipe should enter approximately 1/3 to 2/3rds of the depth of the fitting easily.
The last things before gluing are to make sure the pipe and fittings are clean and dry. Moisture can effect joint performance, there are "wet-R-dry" glues available for cases were you can't be assured the pipe is dry and they should be used in those cases. Secondly, the "duaber" or applicator, should be properly sized. It should be approximately 1/2 the size of the pipe your gluing in order to get sufficient coverage. Personally, I use a 1" dauber for everything. It's perfect for 1-1/2" and 2", a little small for 3" and 4" (sometimes I'll have to double dip) in the cement, and a little messy for the small stuff.
On to gluing.
Using the proper glue is essential. My local supply house carries the IPS/Weld-On brand so I will refer to it. I use the "P-70" primer which is their premium level primer and is also good in cold weather situations. For glue, I use the "705", it's a high strength cement that is good for Sch.40 pipe up to 6" and has a fast set time. For a slower set time in hotter weather I would recommend the "711". When using flexible PVC I use "795" which is also fast set but forms a more flexible joint. When joining PVC & ABS I use the "794" which is a transition glue. For any of these glues if you see the number 2 in front (ie....2705, 2711,2794....etc.) it's older stock, IPS went through a label change a year or so ago.
Most building codes require the use of purple primers as an indicator that they where used, though it's true that cement alone can create an adequate joint. I highly recommend using a primer, whether it's purple, or my preference, clear. Possibly contrary to popular believe, primer is not for cleaning, it will clean, but it's primary purpose is to soften the plastic in order for the cement to fuss together the joint easier.
To begin gluing the pipe together start by applying primer to the fitting socket, don't be shy, you want to work the primer in and soften the surface but don't allow the primer to puddle.. Next, apply primer to the pipe, once again be aggressive in the application, but only for the depth of the socket on the fitting. As a "rule of thumb" when applying the primer, you want to wipe it on hard enough to remove the printed label on the pipe.
After priming the pipe, hit the fitting socket one more time. With the primer still wet apply a thick even layer of glue on the pipe, once again, enough to cover the entire depth of the fitting socket. Next, apply a thin layer to the fitting socket, covering the entire socket.
Now go back and apply a second coat of glue to the pipe before you put them together. With the glue still wet, assemble the joint, giving it a 1/4 twist while you insert the pipe. When you reach the bottom of the socket stop turning. Hold the joint together for at least 30 seconds to avoid any "push out".
After making sure the joint has an initial set, wipe off any excess glue around the joint. This not only make the joint look nicer it allows the solvents to more easily evaporate from the joint.
One last thing, make sure your glue is fresh, if it has turned to "jelly" or is otherwise lumpy throw it out.