Play it while you are concentrating intensely on it and play it when you are not thinking about it and then listen to how it comes out.
Learn that sucker unitl you're sick of it then go away and mess about with the guitar or have a coffee or something. then go back to the riff.
This helps me.
Remember that some days everybody sucks at gtr and some days you can fly.
Try not to beat yourself up about missed timings,etc. If you ain't playing with anyone else then all you have to please is you.
Ponyone's Step 3 is an excellent suggestion.
cheers.
Accuracy,you say? hmm interesting concept..