I've been working with my 22-month-old son on how to take turns for awhile. He's still not consistently giving and taking, and developmentally, that's probably not all that unusual. Still, though, I don't think kids are ever to young to be introduced to the concept of turn taking. Here are some things I try to do with him to teach taking turns.
1) We Share Snacks Sometimes
I'll say okay, you can have a bite, then Mommy gets a bite, and I point out to him that we are taking turns eating.
2) Bathtime
He washes his arm and then Mommy washes his other arm. Again, I'll point out that we're taking turns.
3) Timer
My son is an only child right now (for about 6 more weeks, anyway) but when his brother gets here and gets older, I plan on (if the need arises) to use a timer when they need to take turns playing with or doing something. I have a friend who uses one and it seems to work well with her kids. She just sets a timer and when it goes off it's time to trade toys or activities.
4) Don't Always Let Your Child Go First
I've read this and heard it a million times, but it's still hard for me to take a turn before my toddler. It just feels kind of weird to take the first turn with the finger paints, or whatever it is we're doing. But, I know it proabably teaches a good lesson, so if I think about it, I'll say something like, "You went first earlier, now it's Mommy's turn to go first." He's usually just fine with this, and it does teach him that he doesn't always get to go first.