First, only date people who respect you enough to accept that answer once. If someone is pressuring you to do something you don’t want to do, get out of the relationship. You deserve better! Second, don’t let yourself get into situations where your meaning may be misconstrued. For example, don’t say no when you mean yes.
Second, don’t get yourself into an impaired (read drunk or stoned) condition where you may not mean what you say or may not be able to say no.