It seems obvious that as a domiant you have to be confident. What may be a bit harder to understand is you have to be confident as a submissive as well.
Image your domiant asks you to do something but you cannot bring yourself to do it because you are scared that someone might see you or that you could be judged.
What if someone catches you having sex in a parking lot?
Both dominant and submissive have to measure the risk and reward of their actions. While we might carry fear with us, it is important to look at what we want and need then control our fear by measuring the risk (what if my friends find out that I like BDSM?) vs. the reward (I really like subspace, I feel free there).
Most often our fears are unfounded. Some people might judge you, but they are most likely asking themselves, I wish I had what she has!
As a submissive you have to be willing to step out of your comfort zone. You have to take her your dominant.
Meditation and using small tasks to build up to bigger tasks can help you to face that fear, practice things on your own if you can. Find a place you feel safe to do things that are riskier than you have done in the past, such as masturbating in your car or office.
D/s should be about freeing yourself from all the things we let control us. Set yourself a long term goal and start working towards it in conjunction with your dominant. Make sure they unstand your goal, your hesitations, and your desires.