One of the best things you can do when you are trying to improve your productivity, is to accept less. This is very hard to do, because the more you have on your plate the more productive you appear -- both to yourself and to others. But appearances can be deceiving -- especially in this case. More things to do doesn't mean more productivity. It only really means more things to do.
By taking on more you are spreading yourself out too thin. The more things you have, the more you have to lose track of. The more you try to do, the less you'll you'll be able to do well with everything you do.
If you're trying to accept less, don't try to make it happen overnight. Instead, look at your task and project list regularly and decide to do what's on there "except for _________", and whittle it down bit by bit. By doing this you are looking at what you've committed to regularly and curating what you've committed to do at the same time. You're connecting better with your to do list, and that's a big win. (And you might just avoid what Eddie Smith calls the "coming to Jesus review" more often in the process.)
The truth is by saying "except" to more and accepting less, you'll be setting a whole new level of expectation for yourself --- and those around you will see that. You can rightfully expect more from your life when you accept less.