Please explain how this works even though I'm sure most is due to personal preference.

I ride 46 x 17 and find I spin out sometimes. If I want just a bit more tension in my pedal stroke, what should I do? Chang the cog, chainwheel, or both?

I would ask this at my one of my LBS's but I live in Philly and most (not all) of the people who work in the shops here are self-righteous *****les who would act snarky and then tell me to check online.

Thanks in advance