Determine if your work schedule and responsibilities will allow you to plan time for yourself and your resolution.
Determine if your significant other or other family members will provide positive support to you as needed throughout your resolution time frame.
Determine if you have the physical resources to accomplish your goal. These could include a fitness/performance center membership, proper equipment such as an indoor bicycle trainer, and a workout partner if you don't like to ride alone.
This is a big one. If we revisit Sarah who wants to ride four times per week, she would set smaller markers of success to help her on her three month journey.
For example, she could block out 30 minutes, 4 times per week for the first few weeks then progress to 45 minutes, and finally 60 minutes per workout in the third month. By partitioning a big resolution goal into smaller process goals, Sarah will be much more successful because the resolution goal does not look so immense.
I believe one of the reasons many people do not succeed in their New Year's resolution is because they set a goal that may be so far in the future, they have no checks and balances that allow them to celebrate their successes along the way.