it seems like you don't quite 'understand' the shape, study your apple - it's there to guide you! what's the point in making a still life study if you don't make use of the reference?
a simple sketch makes the whole process a lot easier. i usually keep it on a layer above my colouring so i can see the shape all the time.
if you're going for a realistic look you should always FOLLOW THE SHAPE while colouring, don't draw lines in random directions. Large brushes for block-in and soft blending (i just noticed my tutorials says "smaller brushes" for soft blending, that's a mistake. LARGE brushes!)
nowadays i rarely lower the opacity/flow of my hard/soft brush, i just rely on the pressure sensitivity.
i hope this helps m8 =D
+1..