Two questions:

1. What's your objective regardless of the strategy?
2. Are you strictly in and out with options or are you also holding underlying long?

On the first: If you aim to generate 20% gross, then track that regardless of the strategy. You can easily adjust this simple calculation to compensate for taxes. Alternatively, theta strategies intrinsically have time as a variable. So, I have found it useful to gauge my success on the amount of income I generate per unit time (e.g., per month or per week). You can calculate this as a gross amount or as a percentage of your capital employed.

On the second: If you are interested and willing to hold underlying long and sell covered calls in addition to selling puts and whatever other combination, then you can usually convert your short term-gains into long-term gains.

Consider the Wheel, for example:

1. Sell CSP
   1. assigned? you are on the road to long-term gains (go to #2)
   2. expired? book short-term gains (go to #1)
2. Go long underlying
   1. either just hold for collateral and appreciation
   2. or decide to sell covered calls (go to #3)
3. Sell *qualified* CCs
   1. ITM? roll for a short-term loss
      1. use this loss to cancel your short-term gains
      2. extend holding period -- remember, you are trying to for long-term gains
   2. OTM? book short-term profit and repeat (go to #3)

Eventually, you will decide to sell your underlying lot of be assigned on a CC, booking a long-term gain. Your short term losses and gains should roughly cancel each other and you are then booking long-term gains exclusively.