I found the following useful:
Double buggy
Snacks and drink available for dc1 that they can just grab if dc2 is having a feedathon that you can't escape
Safe activities and books and toys for dc1 to do whilst you're occupied
Swing chair and, later, a bumbo and swizzly toy chair thing to occupy and settle dc2 so you can pay attention to the 1st
Baby can cry for periods of time if needs be, they'll not remember
Think of what needs doing and prioritise them. Put off or don't do tasks that are not necessary
If dc1 still naps, try to time it so it overlaps one of the new baby's naps. This'll give you a much needed rest during the day. If this isn't possible, take them out for a walk/drive til they settle slightly
When dc2's feeding falls into more of a routine, time dc1's meals around them
Don't be scared to use kids' ready meals and quick meals and meals from slow cooker and sandwiches for dc1, at least they're fed and if it's only for a short time they won't fall apart or turn to jelly. Neither will you.
Put dc1 into childcare for 1 or 2 days per week if poss to give you some uninterrupted bonding time with the baby
Keep dc1 involved where possible but don't expect too much too young. And avoid forcing them to bond immediately with the baby, trust that it'll develop in it's own time
Spend some 1-1 time with dc1 every day, even if only ten mins, even if the baby is squawking: resist the urge to go over when dc1 is having this special time (unless necessary)
Keep a safe place for the baby in different places in the house, away from marauding toddler, so you can deal with other things eg cooking, phone, door, toilet etc
Keep up with behaviour techniques for toddler where possible but pick your battles and decide whether it actually matters. Dc1 will prob engage in loads of attention seeking behaviour so only give attention to what matters. And give plenty of positive attention for behaviour you want to see.