Yes, have fun with your colors! Don't be afraid to use certain colors that you have always stirred away from. Some of the colors that are commonly avoided are yellow, green, and orange, which in my opinion are amazing colors to work with when putting an outfit together. You never know, they may just be your closet's new "best friend".
Yes, layering is fabulous! Again, playing with colors and layering is a great way to put an outfit together especially when you are in a rush and need a quick fix. Layering can also make a piece look absolutely amazing.
Yes, black is the best color to mix with. I have to admit black is my closet's "best friend" and silver is right behind. You can't go wrong with wearing black unless, in my opinion, your whole outfit is BLACK. You should only wear all black if you're going to a funeral, but even that is pushing it a bit. You need to mix it up with other colors.
Yes, accessorize! Please don't forget to accessorize that nice outfit you have on with a pair of cute earrings and a few bracelets and/or a cuff. As for me, Spring and Summer is when I accessorize with my popular flower/butterfly hair clips. I normally don't leave home without one in my hair.
Yes, you should make sure your hair and make-up goes with what you are wearing. I mean if you are going to the gym or going for a run, are you really going to have your hair and make-up done like you're going to the night clubs?? Oh wait...there are a few unfortunate ones out there that do this but please try your very best not to because it just looks ridiculous. If I'm wearing something with a purple, I like to add a hint of purple eyeshadow but try not to overload it. Less is always better. Of course if you're wearing yellow, I wouldn't advise you to wear a hint of yellow eyeshadow, that would just look tacky. I would work on natural colors (bronze/brown).
These are just a few of my "Yes" suggestions. I have some pictures down below that help people visualize what I have addressed in the above paragraphs.