Since I started this, my goal has been to deliver quality material with quality service. I don't want to be the type of photographer who treats this as a job, but rather treats it as a passion. With that being said, I've found that being professional really makes an impression on my clients. I think it's really important to talk to your clients one-on-one before the shoot, whether it be on the phone or in person. Take the time to get to know them a bit and establish a friendly relationship. It helps to break the ice before your shoot and things will flow much more smoothly.
Have patience during your photo shoots. If someone decided to book a 1 hour session with you that means that, out of all the photographers in the area, they chose you. Don't be the kind of person who charges your clients for breathing. If they go a few minutes over the the hour just remember that photography is your passion and it shouldn't be big deal if it takes you a few extra minutes to get some more great shots. Never miss a great shot because the hour is up. I hardly, if ever, check the time during a photo shoot, and I'm sure your clients will know if you really want to be there or not.
Last thing I have to mention before I wrap this up is punctuality. Always try to be on time or at least a few minutes early. There's a few advantages to being a few minutes early. The biggest one, obviously, is that you don't give your client a bad impression. Second, you get to scope out the area for any potential spots. It helps you be a little more prepared when your clients arrive and you wont be wasting time looking around for good areas. Lastly, it goes back to being professional. You are representing yourself and your business so just be on time.
Clients really do notice these things. I know because they tell me themselves. They appreciate the time you put into their shoot and its a very rewarding feeling when it is noticed.