preferably

Preferably means that if there is a choice, this is the one to pick. Not compulsory — just better.

It softens an instruction into a preference, which is why it turns up in requests and specifications: bring a jacket, preferably something waterproof. It usually follows a comma and introduces the preferred option. The verb prefer takes to rather than than, so you prefer tea to coffee, which is a common learner error. Ideally does much the same job and sounds a little less fussy in speech.