EMC

Do not make one common ground. Instead, you should make a separate ground for a noisy circuit like VCO.

Board designing is a fairly involved exercise.
What are you designing?
A digital or an analog only or a mixed signal board.

Of these Analog only board is quite easy for grounding purposes. For mixed signal and high frequency digital boards special care has to be take care of. Some fundamental principles are

1) Isolate Sensitive components
2) Make sure that grounds are not shared between high frequency and low frequency devices. The Vcc should be properly filtered.
3) Bypass is a crucial element.

For specific problems PM me.

This is a special subject in RF PCB design field, which disturb RF designers. There are many articles describing the problem on website. More practice, more skills you'll master. Good lucky!