Second time round I found the baby a doddle, but managing DC1 was the challenging bit. It's probably easier if your DC is at school in the day. My second baby was also just an easier baby, luckily for me!
Get out every day. Have one thing every day you look forward to (even if it's a square of chocolate, five minutes alone with a cup of tea etc). Get in easy food. Get in stock of amusements that will keep older child entertained and have them up your sleeve - DD loved sticker books, if I could whip one of those out on a challenging afternoon, we were saved!
If you have a garden and your 5yo is the right kind of kid, think about getting some outdoor toys or equipment when it's warmer - I used to sit bf while DD played in her mud kitchen, balanced on a plank between two bricks etc.
See if any other parents you know might be able to help with the school run now and then if you need it. If your DC has any school friends with young siblings, do some playdates so your DC gets a few clues what it's like.
Use a doll, books, TV programs to tell your DC about babies, what routines they have, how they're different from big kids etc. See if you can hand the baby over to someone and have 121 with your DC regularly, even if it's just for ten minutes before bed etc.
Have a think about what you'll need to babyproof in future, if this includes DC toys like small lego pieces, have a plan for this so you don't all of a sudden say 'you can't play with this because of the baby' - get in the habit of keeping things with small pieces on a play table etc that can be put away.
Have places you can plonk the baby down (bouncer, sleepyhead thing etc) so they can be watching you but you're still hands free to play with DC1.
Don't freak out if DC1 doesn't seem to love DC2, think of it like your partner bringing a new wife home!
Have something that takes you out of the baby zone mentally - I used to read books on a kindle app, listen to podcasts etc - something that reminds you the world is still turning!