The stock preamp tubes in the Valveking already are pretty high gain, so you won't get much change there. With my Valveking, I swapped the preamp tubes out for some JJ ECC83's (12AX7) that I had laying around, and swapped the power tubes (the stock ones are the worst I've ever heard) out for some Ruby 6L6GSTR's. I also swapped the crappy speaker out for an Eminence Wizard. I also tried a Governor, which is supposed to be very similar to a Vintage 30, and hated it! The Wizard really opened it up, and tightened the bottom end up, and made it louder. The tube swap was also a big improvement, giving it a punchier and meaner tone. I usually run it with the Texture knob completely clockwise (to the right), and the resonance button set to tight. At lower volumes, you might prefer it set to loose, and the Texture set closer to the left side. You'll just have to play with these two settings to see what you like best.

The Valveking is really a good amp for the price, but with a tube and speaker change, it can become a great amp! You might also want to invest in an EQ pedal, and an overdrive pedal. This will help you shape your tone, and give you a gain boost if you need it. I use an MXR 6-Band EQ, and an MXR ZW-44 overdrive. If you don't want to spend as much, I've heard some great things about the Danalectro Fish 'n' Chips EQ, and the Boss SD-1 Superdrive is extremely close to the MXR ZW-44. Try using the EQ in front of the amp, and also in the effects loop. In front of the amp, if you boost any frequencies, you will naturally get more hiss, and this is just going to happen when boosting the front end of an amp. However, this is the quietest amp I've ever heard, so it's never been a problem for me. I'm not referring to volume either, just the hiss that some amps have.