Try to figure out the following:
Is it a ring oscillator or an LC oscillator?
Does the system architecture demand a single-ended or a differential oscillator?
What is the maximum allowable power dissipation?
What is the phase noise specification?
What is the supply voltage you are designing this VCO for?
What would be the gain of the VCO?
Frequency tuning range?
Do you require individual phases out of the oscillator or do you just need one (differential) output?
When you hve figured these out, you would be on your way.
Best of luck