In addition to the other good advices you have received, I suggest you focus on what devices you want to protect from substrate noise.
For example if you want to protect the p-mos transistors inside the n-well, then you want to reduce the noise coupling through backgate modulation and capacitive coupling through drain and source reversed biased junctions. Thus, you want to connect the n-well to the same positive supply that powers these p-mos transistors and through a very low resistive/inductive path and using multiple n-well contacts (no RC filter here).
You can analyze similar cases in a similar way, by first identifying the coupling mechanisms. An RC filter for example will block some frequency components of the noise, but before you implement it I suggest you identify what noise you block, where it is coming from, and what is the impact of how do you block it (charge displacement in the capacitor generates transient currents; where do they go)
Cosmin Iorga, Ph.D.
NoiseCoupling.com
http://www.noisecoupling.com