Normally you would wanna stay in Subdivide Collapse mode for roughing out the overall shape and form, giving the appropriate geometry density to where it needed.To fix the lumpiness,in Collapse Edges mode, you can try the Flatten + Smooth brushes then use the Grab brush to move and straighten out uneven edges, make sure to move around the viewport and check it on every angle and zooming out to have an overall view of your model from time to time. You may also want to have a look or re-visit Kent’s “Sculpting fabric” video to warm you up.
Your model is shaping up nicely, keep up the good work 😉
