I usually give my stateroom attendant, who are always excellent and extra $20 for a 3-4 night cruise.
I haven't take an 7 night in along time. It would depend on how many in the stateroom etc. Maybe $50 extra for 2 people.
On my 3-4 night, I usually give head server $20, assistant $10-15 or a $20 if I am ordering lots of cocktails. This is for 2 people.
I always bring cash, put it in the assigned envelopes and give to them on the last nights dinner. And of course I let them know how much they are appreciated.