Lebanon is a modern and cosmopolitan country. It is however important to recognize some local culture and values. A lot of this is common sense, however below is a list of things to consider:-

Attire:

Wear casual clothes during the day but nothing too revealing
At restaurants and venues in downtown wear more formal clothing rather than casual attire
Lebanese tend to stare a lot at what you wear and what you look like, it is normally acceptable behaviour
In remote towns and villages dress conservatively

Tips:

Tip waiters and waitresses, normally 10% of the value of the meal
Pay valet parking attendants no more than 5,000LL (approximately $3)
Taxi drivers usually ask for a tip after they have performed the service. Its not necessary to give them anything, but if they ask add 2,000LL ($1.3) to the overall fare

Body Language:

Its normal for people to greet you with a handshake or 3 kisses on the cheeks - alternating. Do the same if you feel comfortable
Public affection between couple is unacceptable. Its ok to hold hands with your partner but thats the extent.
Don't show the sole of your feet to other people
Please remember that observant muslims may not shake hands or engage in any body contact. Please be respectful of their wishes.

Religious Ettiquete:

Don't enter a mosque during Ramadan or when a service is being held
Ask permission to enter a mosque (if you're not muslim), and remove your shoes before entering
Dont take pictures inside a mosque or a church
Don't talk loudly outside a church or mosque when there is a service or call to prayer

Gifts:

If you are invited to someone's home for lunch or dinner it is customary to bring a small gift with you, box of chocolates, flowers etc
Do not receive gifts from people on the street