It's very hard, honestly. But, it can be fun at times since they usually like the same kind of things. I just hold on to the promises of others that it will be great when they are older. I hold on to that. Get organized now if you're not already! No major project will get done for a long while which makes everything worse (if you're doing a project). If your household is organized now, then all you have to pay attention to for the most part are your kids. Once your newborn become a toddler, things get a little easier.
Have things handy for your son. He needs to be able to get to his own diapers and wipes, shoes and socks, etc. He needs to be able to reach diapers/wipes for your newborn. That will be a great help when you need something that he will be able to get for you and bring to you. It will speed things up and he'll be pitching in. I would even have outfits put together. He could go get whatever he needed and at least bring it out to me to help him. Fold up his diaper (or in a bag) and teach him to throw his own diaper away. Once he knows where the trash is - it will help a lot. Keep bags for dirty diapers where he can get them for you as well.
Before you start breastfeeding or napping or something that you don't want to be interrupted in, make sure you set out a cup and snack for him in a reachable place, as well as toys. That way, when he is all of a sudden thirsty, all you have to say is where it is.
Enjoy the amazing bond between the two. It is sweet. Once they hit school - the relationship won't be so nice to savor.
At the beginning, use a baby carrier backback thing. I loved mine. I could go anywhere and the baby would just fall asleep on my chest. It leaves your hands free, at least one to hold the hand of the other child or push the cart or stroller. Once older, invest in a double stroller.
Enjoy!