Setting tasks, from housework, to other forms. You could inspect how well they have been performed and reward and punish when needed.Remind the sub that it is also a reward for them to do these tasks for you, first off they are sorting out YOUR things, and secondly a clean home or area can prevent stress. If you want to be extra cruel, once they have cleaned, if it hasn't been done well enough, make it messy again. Or if they are to make you a drink, and it's not perfect for you, tip it away straight away.
Kissing denial can also be fun. Tell the sub you aren't going to kiss them, and for the time during this, tease them by hoovering your lips near theirs, you can pull there hair (however hard you agree, but doesn't have to hurt, just performed as an action). This will get them hot under the collar. But please note, it's not a game to play when on a moving bus - I found out the hard way, although he sub felt very happy happy for the bump in the road....
Using them as a foot stall. Although the last person who did this for me, I did comment on how their legs and arms need to be shorter as they were too high for me to be sitting comfortably. I'm a tad harsh at times, but he just found it funny.
Forcing to make them wear something they dislike, it doesn't have to be the op. sex clothing. As a reward you can let them take off a piece. You can comment on how nice they look in it to confuse them, or comment harshly about how they look silly - it depends on the situation and the person.
Taking things away from them or restricting them from certain things they enjoy, and then giving back / allowing access when they deserve it.
I could go on actually, there's lots that can be done.
Have you also tried mixing up massage with the odd surprise scratching or rubbing other textures and tempuratures onto their body? That can be fun.
