You will find out that people use several methods to determine this. My method is to just look at the site and price accordingly. There are many variables to consider with each yard. I like to average $45-$50/hr. in mowing.
You should also set a minimum price you will charge. A lot of guys use $25-$35 as a minimum. As long as you price according to what your area is accustomed to you will be ok. Ask around and you will soon find out what the going rates in your area are. Good luck.
mowing and mulch by the square foot with minimums. Everything else by the hour. As far as how much.....well don't really want to post that if there are other competitors lurking around. I can say that I am not the cheapest guy on the block.
Ok I'll answer you the best I can if your new I'd learn to charge by the sq ft this will teach you the right way and keep you from hateing any of your jobs and keep you out of the poor house. As for how much to charge in your area that is a different story. You will have to either ask around and hope there are some nice LCO's in your area or by trial and earror nothing teaches you better than experience, but when you charge by the sq ft there are many other things to consider. How much trimming, edging, blowing, and if there are any bonus jobs. Mulching, pruning, spring and fall clean ups are just a few and they can add up to alot of extra business. Also on the cheaper (low baller thing) most customers that you will keep as a premant customer will like quality more than the cheaper price. The ones that always take the lower price will replace you as soon as they find a lower price.
Sorry after seeing your profile I see that you have been in business for 3 years but I still think the info that I gave you is the best also make sure that you are charging enough to cover your expences and still make some for yourself noone wants to work for free no mater how much you love this type of work.