It is very common to be invited out for lunch or dinner in Malaysia as business entertainment performs an important function in the all-important relationship building process. (Business breakfasts would be much less commonplace.)
Although it is not always the case, most detailed business issues are left to the confines of the office. It is a good idea to try to use the meal as an opportunity to broaden out the topics of conversation and develop your personal relationship more fully. Good topics of conversation might be Malaysia as a country, mutual acquaintances, food and sport (football is very popular.)
Whenever eating, passing or receiving food, use the right hand as the left hand is considered to be unclean. (This rule applies even if you are left handed.)
Malaysian food can be very spicy but less spicy alternatives are available. It is polite to leave some food on your plate as a sign that you have been well satisfied with the amount of food provided.
Remember that many Malaysians are Muslims and may not, therefore, drink alcohol and will definitely not eat pork. Most people though (unless very orthodox) will not object to you drinking alcohol.
In Malaysia, in a system that the locals call “plus plus,” a 5% tax is added to bills of hotels and restaurants classified as tourist class, along with a 10% service charge. You can add an additional gratuity if you wish (5% is usually adequate) but it is not absolutely necessary.