When looking at Theta, remember that it decays exponentially increasing substantially as expiration approaches. Also selling puts is a very effective strategy if three steps are implemented: 1. The options are sold on something you want to own, 2. The capital is set aside to purchase the underlying if assigned, and 3. It is part of a long-term strategy with the expectation that it will be implemented multiple times (dollar cost averaging). Personally, I only sell puts on indices since they have an upward bias, are cyclical and have a negligible probability of becoming worthless (such as in a single stock). If the above is applied correctly, you will never have to worry about market direction again. Best of luck.
The easy simple answer is for you to get some type of options analytics software that will allow u to view a risk graph and see exactly how a change in time and the other greeks will affect your position and profit and loss potential. Thinkorswim platform is free and you can download a demo account for free.