what are tuning dots and how to effectively use them
Their purpose is to provide a means of adding variable length stubs for impedance matching.  A wire bond can be connected from the bondable gold surface of the microstrip center trace to the pad.  The bond wire will have an inductance value based upon bond height/length and wire thickness; the bond pad will have a known capacitance based upon the substrate dielectric and the pad geometry.

A very brief mention of their use can be found here.  Additionally, their use is discussed at Microwaves101, where they are called "chicken dots".