Identify all your local resources: playgroups, decent parks/playgrounds, library, swimming pool, sure start etc. and find out what they offer for toddlers. If any take your fancy sign up.
I personally find it is easier to have a few scheduled things: (at the moment we do Tues swimming, Wed music class (both with Mummy) and friday two hours of pre-school (away from Mummy), they may only use up a few hours of the whole week but they do give you something to plan around (and get you out of the house mixing with other people!). Also good to leave yourself a couple of days with nothing on so you can plan day's out or invite friends over to play.
Identify what times of day you can get out and do things, having regular lunch, dinner and nap times will make this easier.
Have a mental list of activities you can bring out if stuck at home, such as playdoh, puzzles (keep them in a cupboard so they are 'new' each time), baking cakes, lego, sticker books, colouring, magnets on a baking tray.
Try and keep the house generally tidy as you go and just blitz once or twice a week, if they are keen get kids to help with clean up, dusting, sorting washing, recycling etc.
Kids also like running errands so take them to the post office, bank, supermarket etc (just not everyday or they will get bored quickly).
Have decent rain gear for all of you so you can go out in any weather.