Your yeast could be dead: If you finish step 1 and after 10 minutes there are no bubbles present, your yeast is dead or the milk possibly was too hot. Try again with a new batch of yeast and/or cooler milk. Check out this post on yeast for more info. Not kneading the dough long enough: This causes flat and dense donuts once cooked. The kneading process develops the gluten structure. It will make the dough more soft and elastic. Not proofing the dough long enough before frying: Make sure the dough doubles in size the first time you prove it. For the second proofing, softly poke the dough with your index finger. If it leaves a small indent that slowly springs back (but not fully), they are ready. It it springs back quickly, it needs longer proofing. If it collapses and doesn't spring back, its over-proofed.