Relationships are not limited to physical contacts, nor their goal is to have sex. Long Distance can give you the opportunity to focus on things that matter the most in your relationship. That being said, I believe LDR can challenge a relationship towards better, but can’t solely damage it. Compared to a regular “no distance” form of a relationship and as mentioned in other answers, the most important difference in LDR is the significance of trust! But trust is not something you simply have. It is something you gain, verify, and maintain. This is the same case in regular relationships as well, but the way you gain, verify, and maintain trust in an LDR is different:
Communication: Talk, text, and e-mail a lot. Talk about everything from your daily activities to your inner feelings and thoughts about everything. Sometimes it is good to send emails. For example, in case of time difference, you can send emails while your partner is sleeping, so that s(he) can read it in the morning.
Never lie! not even white lies to impress her/him. LDR is not a good place to impress your partner by not showing your true self.
Involve your partner in your daily life and ask him/her to involve you in his/hers. Do things together, such as watching a movie, reading a book, etc. Spend time together too much until you start feeling that you are not spending enough alone time. Then encourage each other to spend some quality time alone or with friends out of relationships.