I am really trying to curb some behaviours in and get a little help (basic things like putting your clothes in the laundry basket, or your towel on the rail).
I have tried reward strategies in the past but they don't seem to have worked out well at all. Either they don't achieve the reward because the effort isn't there or they ask for massive rewards that are not proportional.
We started a basic reward system at around that age to get dd up and ready for school in the mornings. If she got up when called she got a marble. If she was ready to go to school before me more at the same time, she got a marble. And there was a third thing. We don't do tv during the week but once she got 15 marbles together she could watch for 30 minutes. If she saved up to 20 marbles we would go out for a milkshake. I realise that these things may not motivate your ds, you will have to figure out what will really be a reward for him and acceptable to you, then set things up so that he gets the reward without waiting too long. If for example you are giving a marble for clothes in the laundry basket I would remind him the first few days so that he can see the number of marbles in the jar increasing.