Well yellowing tells me that there is a lack of Nitrogen but, don't use synthetic fertilizers. Get some manure and some compost and repot the plant using this mix and the existing soil as the mix. Bury as much of the stalk as possible pinching off the lower branches.
With regard to watering, stick your fingers in the soil to see how damp it is, once it dries out a little give the plant a good watering and then leave be testing the soil daily.
If you can find it, Kelp meal is a great ammendment as well. A handful will do a plant for the entire season as it is slow release.
Feed the soil, not the plants.