DOs and DON'Ts in mobile game development

as the title says, what I have to do and what should I avoid in mobile game development (especially iOS and Android) cos sometimes there are games with simple textures, low quality graphics, and the size is only 10-20MBs, but the game is very heavy, its lagging everytime.

things that I just know are

• don't use onGui.

• override textures for mobiles

are there any more rules on developing mobile games so that the game is not lagging? thanks