A nice rap beat does not have to be complicated and have a lot of different sounds
. Sometimes less is more if you can create quality in what you're doing. A good beat is not necessarily the one with the most instruments. A nice rap beat is the one where the beat moves you, people can naturally nod their head to it and your artist is inspired to 'spit' on it in a unique manner.
When you create your rap beat you want to reach within you for inspiration. I'm not saying that you cannot be inspired by other producers but you don't want to copy another producer. In some cases creating that nice beat will inspire you to sample and that's okay providing you bring something new and fresh to the track.
You may find it helpful to collaborate with your artist or someone else that has a good ear for music. People are your best and worst feedback because if they know you they may always say something nice so you should try to get feedback from strangers. In the internet age this is quite easy because all you would have to do is post your track online and ask for comments. People will definitely tell you what they think. I hope you have a thick skin.
If you're wondering exactly how you are going to go about creating that nice rap beat you have many options. If money is an issue you can use a good online beat making software that will allow you to use it 24 hours a day 7 days a week. You won't believe how reasonably priced these type of software can be. And you get a lot of the same features that you will have access to in a traditional recording studio. And don't be worried about learning to use it either because you will have access to video tutorials and written instructions.