I am not and expert and I do not know all things about photography. All I know is what works for me. Most things that I have learned have been from trail and error and lots of practice. But one thing that I have been working on is how to get sharper and crisper images.
Theses are just a few tips:
I try to always shoot in natural lighting. I love the way that it looks and it creates great photos. If my session is in the middle of the day and it is too sunny outside, I look for open shade.
I do not use the auto settings. There is a noticable difference between auto and manual. It gives me full control to make my images as sharp as possible.
I also try to keep my iso as low as possible. A higher iso will make the image look grainy, so when I can I try to keep it between 200-400.
Having a fast shutter speed is very important for crisp images, especially if you are not using a tripod.
I love to shoot with a low aperture. This is just my style and preference. It gives me a nice depth of field, but unless I have a steady hand (something I practice) it can create blurry images.
Learning how to focus your camera correctly. I use single point auto-focus because it allows me to choose what I want in focus. And for portraits it is almost always the eyes!
I had to learn how to hold my camera steady. Because I like to shoot with a wide aperture and in natural lighting, if my camera shook just a little, it was noticable in my pictures. It might sound silly, but I even practiced my breathing so that it wouldn't effect my images.
Equipment. Although the equipment is not what makes good photos, I noticed a huge difference when I went from an entry level dslr camera to a professional level.
I also had a huge improvement in my photos when I learned how to edit correctly. Picassa and Picmonkey are great for fun and quick photo edits that you take on your point and shoot camera but it eliminates any sharpness in the photo.
I mainly use Photoshop for all my editing but have heard great things about Lightroom as well. You can download a free trial version or if you are a student or teacher, you can get these programs at a discount. Lightroom is at a very reasonable cost, too.
Most importantly is practice! If you love it and want to improve, don't ever stop practicing. I am still learning and improving everyday. I just try to do my best and learn from my mistakes - I have had many. I just love it, so I'll keep working at it!