Groove is god in Hip Hop. "If you can't feel it, it ain't right." Assuming you already have a groove, you will need to properly mix it. The first three words you should know are: bass, bass, bass. The bass (or kick) drum is the heartbeat of the entire process. It needs to be deep, but distinct. Using a compressor and/or a limiter combination and jacking the frequency to 12 o'clock will add punch and separation. Be careful not to use too high a ratio on the compressor as it will make your kick drum sound small. On your EQ, do not add lows. Use a zero sum mentality, which means pull back on the highs and mids to achieve a deeper sound. Increasing lows will muddy your master mix. If you are using software such as Cubase, Reason or Logic, there is a mixer interface on the program; you should be able to use limiter combos in tandem. As a general rule, roll off highs and lows on snare. Roll off mids and lows on high hats. Tweak the EQ until you feel the sound is just right, your best assets are your ears. Mixing the drums prior to mixing your other tracks will save you time in the long run.
Hip Hop vocals are mostly rhythmic and therefore necessary to keep the spaces between the words clean. Make sure you get a clean input, i.e. there should be no background noise that cannot be edited away. Use a pop filter on the mic, or the hisses and pops will be too hard to mix down. The mix is going to depend wholly on the voice of the singer rapper. Start with the EQ: roll back highs, then lows, then mids on the three-band EQ to see what gives you the clearest tone. If you are using digital software with an audio wave view, use the interface to erase noise in between, which will increase the vocal rhythmic intensity. If the vocalist vacillates in volume, an isolation compressor should be used on the track before the end chain (master) compressor. Experimenting with reverb and delay will give the vocal depth, but be careful not to add too much as it becomes amateurish if too many effects are layered. Keep in mind a clean take is the best recipe for a successful mix.
After you have mixed volumes and EQs, put a compressor at the end of the chain. This will keep your tracks from clipping when mastering. After the compressor, using a maximizer will give you back the punch the compressor took away without the fear of clipping. All effects units should be run in front of the compressor and limiter so that they are controlled. The following is an example of how DJ BG sets his compressor for Hip Hop recordings where the mix has been peaked at -3db:
Gain 3.5 db
Threshold -22.6 db
Ratio 3.00:1
Attack 11 ms
Release 50 ms
Knee 80