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Lots of groundplane, dont have breaks in it, dont have breaks in the return path of noisy/sensitive signals.
Keep sensitive signals away from noisy ones, find out whats generating the noise in the first place & redo that section of board (if not all of it).
have atleast one solid plane to reference the signals.
keep it closer to pwr plane(if it were gnd)
add decaps wherever u think noise would appear...(this is just a brute force method actually u ll have to calculate the decap vaule and decide the placement after many simulation iterations)