The best time to visit Morocco is in spring (March - May), when the country is lush and green or in autumn (September - November), when the heat of summer has eased.
Other than the weather, the timing of Ramadan is another important consideration as some restaurants and cafés close during the day and business hours are reduced.
Bargaining in souks is natural part of the culture and is always expected from a potential buyer. Always ignore the first price a merchant offers.
Tipping is common in Morocco. Between 5% and 10% of a restaurant bill is appropriate. You can also tip taxis, guides and whoever helps you. Don't tip too little (less than 5 drahams) as it may be seen worse than not tipping at all. Rounding a bill a little up is also a good option.