First of all, if your foreskin and penis head are still attached, try to push your foreskin backward until your penis head can completely come out and get separated from the foreskin. If it is too painful for you, then you should see a doctor for circumcision. Then make an OK grip around your penis head, and stretch your penis.
I'm new at this too and also uncircumcised. I discovered it helps to pull down to hold things down and then work as perscrped but alternating hands every seveal strokes so you are getting the same effect as alternating every time and you can have a good hold.
Also if you have any hair that gets caught do a little trim or shave to keep it from getting pulled which was a problem I was having.
I wouldn't reccomend a circumcision as an adult inless there is a real medical need. i didn't even put my son through it when he was born.
Try what AvgJoe said... no, no; not the circumcising part. We'll call that plan B.
With either hand, try pulling back the foreskin until you can completely see your penis head. Hold that excess skin in place and pull. Let us know if you have any problems. There's no reason to go to plan B just yet.