As you are only at eighteen , It’s a good idea to start a good one, and at low rate, You have a lot to study in the business field, Don’t expect a big success at first.

ok here is what you do. you have the stuff cards and a truck i hope. but do you have bags to bag the grass. or a work permit? if yes than you just need to get a trailer and try to cut for wealthy people. make sure your a descent cutter, have money to replace broken parts and youll need gass. so have fun. from one weed wacker to another

Make sure you and your partners make up a formula for a quote on someone’s lawn.
For instance, a certain price per square yard. Do this for every type of job, and decide whether you need to consider the size of the job or whether it will be flat rate.
Open your options. If a customer asks you to do some type of work that you haven’t done before, give it a shot. Keeping them satisfied is the key to success.
Also, if a customer wants their lawn cut every thursday, be there every thursday. Friday will not do.
If you don’t have a trailer I wish you the best of luck, traveling from client to client will be tough.

do a good job and start with a low rate, you will soon have all the work you need ,
after you establish plenty of work than you can start slowly raising your rate to be more inline with your competition.

I’d start off pricing at market rates but try to offer a premium service.

Put time into branding and marketing rather than working cheap and build up some quality clientelle rather than bargain hunters. Look into Craigslist advertising and other free methods.