Thumb gussets & fingers on gloves

I am attempting to make gloves and I always seem to leave holes when adding stitches to create the thumb gusset and when creating the actual thumb and fingers how can I not do this?? Help!

I haven’t made gloves, but have made mittens. When I make the gusset, I make an extra stitch at each end of it so I can knit two together with stitches from the hand. It seems to help.

Here’s a good tutorial: