Always match a monster's color with a similarly colored room to earn bigger tips. If you do it quickly you'll score even more cash.
Watch out not to fail to satisfy a monster's request or to do it fast enough cause it'll make the guest angry and he'll leave the hotel. All this negatively affecting your points and tips.
With level 5 you'll gain access to worm cakes if you leave them in front of rooms before monsters check in it'll boost their happiness.
Smart move would be to buy Blood Drops before starting a level and place them in front of rooms. The more Blood Drops a room has, the more Blood Bills you'll receive.
Save time while loading Dracula's cart with several items.