reduce vco phase noise
do some noise calculations by hand to see the noise contribution being injected into the tank. Should look at flicker and thermal noise mainly. If you are using cadence then the noise summary will list your individual device's noise contribution. then just minimize noise accordingly using equations found in most texts/lecture notes. An example would be say for flicker noise from your tail current mirror (if you have one). Usually this flicker noise is huge and gets up converted into the vco, one way to reduce it is to increase (W*L), another way is to reduce current, but current will if designed properly reduce your swing thus decrease phase noise even more so best is to increase the transistor size of the tail for flicker noise. Alternatively you can add a resonator which shorts all low frequency current noise generated by the tail so theres no upconversion. Transistor sizings will depend on which type of noise dominates in your circuit, increase gm to minimize voltage noise, minimize gm to reduce current noise. Use fingers to reduce gate resistance hence thermal noise. When you've optimized all the elements, the mosfets that make your -ve resistance should dominate noise contribution, then its a trade off between startup/reliability and noise injected into the tank. As rania said, increasing current will increase swing and reduce phase noise.