When bubbles begin to rise, or when you see the oil beginning to "move" across the bottom of the pan, it should be ready for frying.
Tip: If you're not sure when oil is ready, try dipping the corner of a cake into the oil. If nothing happens, it's not hot enough yet. If it begins to sizzle and cook, it's ready.
Once oil is hot enough, keep your dial around #6 (closer to medium than high heat). Carefully place cakes in the oil. Fry 3 or 4 cakes at a time. Note: You can use your tongs to place the cakes in the oil, or carefully "drop" them in with your fingers - just be careful not to touch the oil.