Well my dd2 was born when dd1 was 1year 3days old so we had them very close.
The things I found the hardest:
Being heavily pregnant and having to look after dd1.
The first few weeks when dd2 was born dd1 decided to stop walking and I had to carry both to & from the car etc.
If your first is already 11mo you won't have those issues.
It is a big adjustment in terms of things like going out taking longer but be kind to yourself and don't take on too much.
Things I used to cope:
Laying out their clothes the night before
Sticking to a routine, keeping it the same for both of them as far as possible
Accept help when it's given!
Go to toddler groups- it entertains the eldest/wears them out and there is always someone who'll want to hold the baby for you.
Try to make any big changes before your bump gets big, like if your eldest is clingy, wants picking up even when nothing wrong, don't wait until you have your hands full with a new baby!
Anyway it is all totally and utterly worth it. There is nothing as good as hearing your children laugh together
And if it was that bad we wouldn't be going for it all over again would we..
Am happy to give specific advice on whatever you want or can just ramble...