Listen to a variety of rap from various eras. Pay close attention to details. Note what types of drums are used. Figure out which beats certain drums are used on. Note what type of sound effects are used. Note what samples are used. Note what instruments are used. Decide what specifically you do or don’t like. As you consider these elements make notes on a sheet of paper. You will refer to this list when you start to compose your instrumental track.
Familiarize yourself with the fundamentals of rhythm. Count along with a track you like. Most music is divided evenly in groups of four beats, six beats or twelve beats, with four being the most common. These groups of beats are contained in bars or measures--and groupings of these bars and measures make up a song. Try tapping your foot, and counting aloud from 1 to 4, in time with the music. This will help you to understand and feel where specific sounds are falling.
Decide how long you want your track to be. It can be as short as 8 bars, or an entire song. You can use the classic pop song arrangement, as this is a common song form for hip-hop, as well. This form is composed of an 8-bar introduction, 8- or 16-bar verse, 8-bar chorus, 8- or 16-bar verse, 8-bar chorus, 2- to 8-bar break/bridge, 8- to 16-bar verse or chorus--and it finishes with a fadeout.
Decide what method you want to use to compose and record your beats. Most music software gives you the option of using an external midi keyboard, a digital sequencer or audio loops. You can also use a combination of these approaches.
Record the drums first, as this is the core component of the song. The possibilities are endless here, as there is no rule in hip-hop as far as how thick, how sparse, type of drums, beats, etc. What matters is that the beat stirs something for the MC to rhyme over.
Record the base line next. It is best to use an analog or digital synth for the bass. The baseline should be relatively simple with a thick, low sound and a sub-base element. This is brought about by filtering and overcompression.
Add in any melodic flourishes, hooks, sound effects, orchestration, etc. that serve the song. You really get to play around here, but remember not to take emphasis away from the groove. Anything you add should accentuate it.
Mix down your tracks. If you recorded a short instrumental track, loop it until you have your desired length and then mix it down. Upload the song to your music player.