Who do I need to hire? How much do I need to spend? How do I get national politicians to endorse me?
The way you become a state legislator is you get more votes in the primary election than anyone else and then you get more votes in the general election than the other nominee. Hiring staff, raising money and endorsements by national figures are all secondary to getting more votes. There are about 40,000 residents in each representative district. Start getting to know your neighbors. Knock on doors, every night, on behalf of other candidates or on behalf of an issue you and your community cares about. And when the incumbent decides to retire or run for a higher office, then you're in a good position to be the next legislator.
I am guessing you have gotten past the initial question you need to answer which is why do you want to run. If so, then the easy answer to your question is that it depends on where you are running, where you are starting from and who are you running against.
You need to look at the district, and where your votes are coming from. You also need to look at where your money is going to come from. Spending will not be a problem, you will be spending everything you raise (unless you are self funding).
You need to figure out your message - pick three key areas that develop your campaign around them. Don't make it too difficult, use your voice - because you will be saying these things over and over and over again.
You will need (not necessarily need to hire, but simply need) a campaign manager, a finance director, a fundraiser, a communications person and a grassroots person. You might need a paid media person, but that can come later. Put a team together - your local R or D committee should have some people who would be interested in getting involved. Friends and family make great volunteers. Don't pay anyone until you have to.
Raise a lot of money. Again - friends and family make great first donors. And a good barometer. If you friends and family aren't behind you, how do you expect to convince people that don't know you. If you are self-funding - know what you are willing to spend. Assume that you will need one more dollar than you have raised. Plan to raise and plan to spend - especially in your first race.
National politicians are not going to matter as much as ones from the Commonwealth for votes, but can certainly help to raise dollars from grassroots groups. How you reach out to them or get their attention varies, so you need to look at them all differently. Make sure you know why you are asking them before you ask.
But be prepared to knock on a lot of doors, attend a lot of small coffees and get togethers. Talk to everyone in your district at least once. Then target your most likely voters again and again and again. If you likely voters aren't going to be enough - figure out where the rest of your votes are going to come from and get in front of them as much as possible.
There are some great political minds in Massachusetts. I am sure you can find someone to help you.
I am happy to do a follow-up call to recommend some people or discuss any of this. Good luck!
All of the answers are correct - also don't assume you'll have party support as a new person on the block. If you haven't volunteered with a party or community organizations then now is the time to start. Connections, donations, doorbells and yard signs (don't let anyone tell you those are a waste of money - we had a county commissioner candidate win by signage alone) - and have your message boiled down in to three easily remembered bullet points.