look at icmaskdesign. Ive just been on a advanced analog course there.
1. plenty of well ties and guard rings. Keep good noise isolation.. tie the gates to signal at both ends to reduce gate capacitance. also use multiple fingers to reduce drain capacitance.
2. use a seperate ground for the substrate . ie star route from ground pad.
3. isolate important signal by placing down nwell, tied to a quite signal or ground. this isolatates it from the substrate. ie less noise.
more important, keep your signal flowing smoothly and make your circuits more symmetric, especially your differential pairs and related circuitry. if you are running some important signal over a ground plane, take care of that additional caps. better you simulate it.