Study up on the genre. It is impossible to make a true grime beat without being completely familiar with grime music. Listen to early classic recordings by genre pioneers including Wiley, Kano, and the Roll Deep Crew, as well as newer material played on the online streams of U.K.-based radio stations such as Rinse FM. If you want to fully understand the roots of the genre, it's also worth listening to some drum 'n' bass, U.K. garage, and Jamaican dancehall.
Sketch out the basic structure of your beat in your software of choice. One of the most accessible beat-making programs is Fruity Loops, so this would be a good place for the beginner to start. More complex choices include Logic, Reason, and Ableton Live. Use the program's built-in drum loops to build the basic sketch of your beat. Most grime music is done at 140 beats per minute, and uses a two-step beat structure similar to U.K. garage.
Listen to your work again and look for gaps. Most likely, the beginning of your beat will be very spare. Listen to it again and try to think about it with a songwriter's ear. Besides the basic drum structure, what added instrumentation or sounds would give it the melodic or mood feel you desire? Hum along with the beats and take notes, if necessary.
Record your own live samples or instrumentation. While there are plenty of pre-recorded sample, drum, and effect packs available online, the best producers record their own original sounds. If you have any instrumental ability, try playing simple melodies or sounds on that instrument, or on a basic MIDI keyboard on which you can modulate the output sound. Record everyday sounds or ambient noise.
Add your original material back into the beat. Take all the snippets you've recorded and decide what you will use. Sample the best part, and turn it into a loop in your music production software. Make the beat truly yours with raw material that no one else has.
Ask for feedback, and seek out vocalists or rappers. The only way to improve as a producer is to get feedback, and collaborate with other artists. Try uploading your tracks to your social media web sites. As of May 2011, a couple of the most popular for aspiring beatmakers and DJs are SoundCloud and MixCloud. Take criticism constructively, and seek out new vocalists or rappers to work with. It isn't a grime song proper until you add vocals, so find some to make your beats come to life.