What Steps Should I Take to Troubleshoot My Gas Oven?
I'd start by checking the valve, make sure it's all the way open.  If the oven has a cook top, you can probably lift up the top and find the valve towards the back where the gas line comes out of the wall and into the oven.

If the gas appears to be cycling on and off while the oven is heating, then perhaps it's a bad thermostat.  

Beyond that, perhaps there's a clog in the burner.  I've never cleaned a burner to know if it's a DIY job, so I'll defer to others for advice there.

As always, when working on a gas appliance, be sure to turn the gas off first before taking things apart.