As cashloans mentioned, reaching out for guidance from a SCORE or SBDC could be helpful. To find your nearest SBA resource partner, enter your zip code at SBA Direct. Also, here's some additional information about partnerships. Good luck!

As CashLoans mentioned, there are numerous issues when you have a
partnership. A partnership isn't a sole proprietorship; rather, it involves
many more issues. You will need to register your business as either an LLC
with two managing partners or as a formal partnership. Then, you need to have
an attorney create a Partnership Agreement that spells out each person's
responsibilities. Without a legal partnership agreement, each of you is
responsible for things the other does or decisions they make, including
financial actions. Too many partnerships end in bitterness and anger because
of the actions of one person. Don't let that happen to you.

Okay, you might guess that a CPA would say something like this... but I would
also make sure that from the beginning you have a simple accounting system
set up and working right.

Probably, all you need is a software program (like Quicken?) or a website
that'll let you track a bank account and then also categorize income and
expenses as you track (like mint?). You might also want to use as your
bookkeeping or accounting program something like QuickBooks because there's
often quite a bit of QuickBooks work you can do for small business owners.
(I'm thinking accounting program data entry might be another "service" you
offer your clients.)

Good luck!

I see that you are from California - know that all states and cities /
counties within the state have their own rules. I would suggest that you
start with your Secretary of State's office
(http://www.sos.ca.gov/business/be/) as well as contact your city's and
county's clerk offices. They will have the specifics for your area.
You don't necessarily need an assumed name if you use your own name.
Plus, you are already a independant contractor just by being in business for
yourself.
Regarding your partner - it would depend on who takes liability and how you
will allocate profits and loss. If you pay your partner but that partner does
not really have any power in the business - the partner is an employee (which
comes with its own issues). If you split profits by some percentage and both
of you have equal say in the business - then, you might think about a
partnership or a LLC. It realy comes down to how you work it all out. Start
by contacting yoru SOS's office or find a local SCORE, SBDC or SBA office in
your area and they can help with your local rules and regulations.