PanamaPilot. I work with many Brokers, and some Shippers. In the event that i need to (which is rare), I negotiate with each of them in the same way. The rate I need at the time, it is, what it is, and they understand that. I've worked with the same Brokers and Shippers for many, many years now.
In my opinion, with you just getting started, you should be focused on seeking out good Brokers and trying to develop a good working relationship with them. Making more money working direct with a shipper is a pipe dream for most Owner Operators. How I made my connections was by always being on time, and always doing the right thing when a problem popped up. No matter who you're hauling for, you always need to represent them in the best possible way. Brokers are always looking for Owner Operators that possess problem solving skills and have a good attitude. Believe it or not, Owner Operators like that are scarce.
Just getting started you'll likely be relying on load boards for work. How you negotiate will make you, or break you. These days there seems to be just as many new Brokers that don't understand the business out there, as there is new Owner Operators that don't understand it. Always be polite, when you see a load you want but the rate is a little to low, tell the Broker you'd like to haul the load but the current rate doesn't work for you . Leave them your name and number. When they realize they have to bump the rate up they'll call the polite Owner Operator back first every time.