That answer will vary by state. If you are in Ga. you first must determined if it will be a single member LLC or Multi Member.
Steps are as follows:
Name Search/Name Reservation $25-$30 (Ga. SOS website.) Look under Corporations then select Name Reservation.
Apply for a new EIN number from the IRS. Its Free
File the Articles of Organization with the SOS. It was $100.00 Seven years ago when I did mines. Not sure if its the same price today. ( you will find all the necessary forms on the SOS webiste.)
Once all this information is filed with the SOS you will have a Legal Corporate Entity.
Apply for a Business License in the City/County where your office will be located.
Apply for a DUNNS# (Dunn and Bradstreet) its free.
Keep in mind you will need to have a Low Voltage License here in GA. to appy for a
Business License. Most contracts requires a Low Voltage License.
Certain counties in Ga. are requiring that you(The Contractor) pull a permit for Low Voltage work depending on the Scope of Work. In order to pull a permit you must have a State Contractors License along with a Business License.
Bring all your new Documents to a bank and open a Commercial Bank Account.
Purchase your G/L insurance.
Now, how you would get a contract with comcast I have absolutely no clue on that one.
Be mindful of the Self Employment Tax that comes along with being a LLC.