A trick I used to learn years ago was to take the bottom half of the rollie (not the half with the glue), and fold a 1/8' (or so) crease along the length of the paper.
This makes a nice little cup for the ganja to sit in, and allows the bottom 'lip' to go easily around the goods, and tuck in. I also use the edge of the rollie pack to gently even out, and lightly press the weed into the 'cup'.
I found I ALWAYS ended up with 'pregnant' joints early on in my joint rolling trials. Doing this, I found, kept the doobie even diameter from tip to tip.
Now, I don't need to do that anymore (the fold), just did it for example. I still 'press' the weed with the rollie pack though. I can now roll joints that look damn near like pre-fab cigarettes.
Must have rolled in the multiple tens of thousands of doobies over the years. The good old days of rolling up a QP and takin' it to the beach.....LOL.
Sorry for the dull pics, the flash is too much, and without is too dark. I feel like Goldilocks when I fuck with this camera sometimes.