Here's what works for my 3.5 year old. A schedule.
Being a teacher, I know that kids thrive on a schedule. They like to know what is going to happen each day...what to expect...it's makes them comfortable to know this. So I created a schedule for my son so that he knows what's on the agenda for the day. It also got him to take a nap since he knew that after his nap he could do other fun things...but not until he took his nap.
On the front I printed the activity and on the back I printed DONE. I glued them on index cards and laminated them. I have them in a pocket chart. He loves to turn over the cards and say he completed the task. I don't add any times for this since I need it to be a little flexible. (plus he can actually tell time by the hour so I don't need that added pressure to keep on schedule that way!!) I also don't use the schedule every day. I want him to also be flexible. Too much scheduling won't allow that.