When mixing vocalsis important to have good compression, and equalization in order to get a good quality sound form the vocals. You can use external hardware for compressing and equalizing the vocals, as well as plugins if you are using computer software. In my case I use computer software knows as protools to work my vocals, so I will be mixing using plugins. There is a variety of plugins that can be use to mix the vocals, I prefer to use Wave plugins.
The first thing you going to do when mixing vocals is to equalize the vocals. You first want to clean all the frequencies that are not necessary in the vocals. For this you are going to use a filter to clean those unnecessary frequencies. Depending on the vocal you are going to eliminate the frequencies. Normally you can eliminate frequencies below the 80 hertz that will give you a good filtering to start equalizing the vocals. Then you want to stand out the presence of the vocals. Usually the presences of the vocals are at the 2k through 5k hertz depending on the vocals. Once you got this done you can start compressing the vocals. When compressing vocals you want to give that power that the vocals are mixing. A compressor has a threshold, a ratio, and a gain. The threshold is the point the compressor is going to start compressing the vocal. After you set the threshold the actual amount of gain reduction depends on the 'Ratio' setting. the ratio setting is expressed in the form 4:1 or similar, and the range of a typical Ratio control is variable from 1:1 (no gain reduction all) to infinity:1, which means that the output level is never allowed to rise above the Threshold setting. These are general recommendations to mix your vocals and a point of references. There is a variety of ways to do it and all depends on the way that you want to listen your vocals. The best way to find out is to work on vocals everyday using different settings to acknowledge the different kinds of settings and effects. I hope this have help you out to have a better understanding of mixing vocals.