Here is what I do. Launch a Sat deployer (crewd if using RT, probe if not using RT) with a coresponding number of sattelites. Get into a stable orbit. Bring the Ap to Geostat level (2868,75 km). Now, we know that 1 rotation of Kerbin takes 6 hours but you could use this information for any planet depending on its rotation speed. For Kerbin I usualy use 4 sattelites as a comm relay. So at Ap i bring my orbital period to 4 hours (can t make it 2 because I would go down into the atmosphere) - MeckJeb or KE help a lot - and then decouple 1 sattelite at the Ap and circualise it to a 6 hour orbit (RCS helps for fine tuning). After 4 orbits of your Sat deployer you have 4 evenly spaced sattelites all in 6 hour orbits. Your relay network is complete. Simple, and low math usage