A couple tips:
ALWAYS install applications into the Applications folder. All apps you get in Apple's App Store already go here anyway; most apps that you might find elsewhere also set themselves up in the Applications folder. I'm saying this because I've seen people store multiple apps on the Desktop; doing this only makes your Home folder bigger and less simple to back up and/or migrate later.
Keep your Desktop clean and tidy. Think of it like a virtual physical desk. Store documents in Documents, photos and movies in Pictures, music-related things in Music, etc. Don't be like my mom and end up with a hundred gigs of nested folders on your Desktop (which is funny, because that's exactly how she "organizes" things on the dining room table).
I use Photos and iTunes to manage my pictures, videos, media, and mobile apps. If you don't want to use Photos, you can use Image Capture to import pictures and videos from your phone and organize them in your own folders old-school-style.
Quick Look FTW.
Take some time to browse through System Preferences, too.