Small bubbles will eventually go away if you set them out in the sun for a couple of hours so don't sweat it but to avoid larger bubbles try installing the base vinyl without app tape. I tape the piece of vinyl down in the middle on top of the substrate and then apply it one side at a time using (once again) a felt squeegee. Then go over it all again with a hard squeegee using firm pressure. Applying vinyl with zero bubbles is an acquired skill that only comes with practice... once you get it down you'll find that it's difficult to do it any other way.

I use a system like speed press, except I make my owne frames and I get the clear tape from fellers, I make a lot of small signs from 6x12 to 18 x 24 and weather I am just using vinyl or full color print and laminated the frame way is it, and sooooo fast. Look up speed press, watch the video then get the speed press tape from feller make your owne frame from window screen parts and wow. I don't tape any vinyl except stickers, just weed, frame, apply and move on, no registration marks needed building up lairs is a snap.

I have several frames of different sizes for different jobs, I use tape on some and binder clips on others. The cool thing is how long the tape lasts, when it starts to get a little less sticky you clean it with water or alacahaul/water mix, I usually get 100 + signs out of a frame before I need to replace the tape, if a frame sits around a while and gets dusty just a quick clean before using and you are good to go.