Make a Schedule
Just like a regular job, you will be required to work a certain number of hours a day. Make sure to limit the promises you make and errands down to a normal, lunch break amount of time. Anything outside of that might effect your sleep, force you to call in delivery instead of cooking, or make you sacrifice work. Don't let staying home all day to work turn into working only four hours around the busy schedule others have created for you!
Sit Them Down
Letting your family and spouse know what you do all day, how important your work is to you, and how long that work can take can help to get rid of some of the tasks your family tries to get you to shoulder. If your income is short at the end of the month, explain that their tiny errands really add up against your time spent doing your job. There are only so many hours in a day and letting your spouse know how your time is used might make it a little harder for them to ask you to help them out during the day.
Practice Saying No
Most of us have been raised to do what we can to please others. It can lead us to shouldering too many responsibilities to prevent guilt trips and bad feelings. But taking time to do your work needs to take priority. Although it might be hard, start small. Say no to that baby shower you have no desire to attend, so no to making the whole kindergarten class brownies, and say no to going out to eat with your sibling. Small no's will help to make it easier to say no to bigger things in the future.
Do you really need to pick up your children from school, or would the school bus be okay? Would it be a better use of your time and money to buy your spouse a few more dress shirts and pants so you can go to the dry cleaners once a week instead of twice? Can you work out from home once a week to cut back on travel time instead of going to the gym? Where else can you cut back a few moments from your day to give your career as much time as it needs to flourish and grow?