Part of your task in the first 90 days in your new job is to build credibility. People need to know that you can walk the walk as well as talk the talk. You therefore need to identify low hanging fruit and early wins. By success you gain backing and build momentum.
They do, however, need to be the right wins. One important person to define these is the boss. A boss who wants pears will not be impressed by a delivery of apples, however low they may have hung.
The other thing to bear in mind is that they should not cut across your overall business goals. If they do, then you destroy momentum, at least in the right direction. And you are likely to undermine your hard won credibility.