The first thing is to really let it rise/ferment until it's done. This can take 2 hours or it can take 5 hours. Depends on the temperature, the day of the week, the attitude of the yeast at the time, etc. So first, get as much gas in the dough as possible because the more air bubbles (CO2 really), the more they can expand and rise.
I'm no expert - I have a hard time with sourdough. I often cheat and add yeast.
I have gone as long as 10 hours after the initial rise. Initial rise after adding flour, salt and sugar to the starter is normal. It seems that after splitting my dough into loaves, there is little to no additional rise. I have tried both stiff and wet doughs and have the same issue with both.
I purchased regular bread yeast to add this next time, as I've gotten very disappointed in just the yeast from my starter.