Like Penny I crop photos with a small trimmer, guillotine style. I don't stick to the "rule" of centering my photos on mats with equal borders, I use photos where they best tell the story and let the art be supporting not central.
I print thru mail order when I can get a deal, and they kiosks when I can't wait! I have spent lots of money on ink and printers and paper, and still wind up trimming them anyway.
One hint to printing the right size is to plan ahead what your LO will look like based on number of photos, sketch etc, and decide if you need to print 3x5, 4x6, or make mini prints and trim or shape from those basic sizes. The photos are always central to me in scrapping. The rest is the supporting cast. I try to limit my really detailed decorative pages and do a few in an album with more that are clean and simple and really focused on the photos and journaling.
I hope our input is encouraging to you. I hope you really feel like you make the rules for yourself and the desire to create drives you to make what is pleasing to YOUR EYE. If it is not fun you won't do it, so keep it fun!
"Find something you are passionate about and keep tremendously interested in it". Julia Child