what is the best way to finance my first investment property?

There are many ways but first understand they all take dollars in hand!  If you have equity in another property you can utilize that but be aware your money is at some risk!  Every investment carries a degree of risk, you have to be able to accept and absorb that risk. 

Without cash in hand or equity to draw from then the best opportunity would be to purchase using a contract for deed, a seller carryback, or other seller financing.  Usually this will need to be a property that needs a lot of work and the Seller would have to be in a position to accept that you do the work as kind of a down payment.  Balancing the risk of no money down from you but maintaining a security position by the upgrades that you do to the property.  Of course this still requires cash on your part because it ill cost omething to fix the property up.