THIS IS AN EXCELLENT QUESTION! for robot designs something I see a lot is just Old computer with funny face (and sometimes humanoid body, or animal-like legs) and while that is not necessarily a bad thing on its own, it can get repetitive. I mostly recommend just changing up the shape of your bot!!! there are tons of differently shaped computer, android, devices etc. out there other than just the standard box-shaped computer i promise!!!!
for character design in general-(I usually design characters paired with some sort of story, but characters with no story and just design can also use part of this) I always make sure each character has some sort of Thing or Gimmick that differentiates them from the others (very vague sounding i know) for example- what is their job? do they have a theme or specific style of fashion? is there something they enjoy a lot that they like to show in their appearance? do they have some sort of Affliction, like a curse or disease, that appears physically? maybe they're a pair with another character--in what way are they similar, but also different enough to tell apart at the same time? A big thing with character design imo is Showing, and not Telling the personality and story of the character--shapes are really important, especially in the face. My art style is more on the cartoony side so I try to give each character completely different shaped facial features. I HOPE THIS HELPS!!!!!