After you decide to run, you have to convince everyone that you are a viable candidate to win the election. Friends and family must be convinced if they are going to give you their hard earned money. Volunteers and activists must be convinced if they are going to give you their valuable time. Party officials must be convinced so that they do not work against you.
Challengers in any race, whether their first or fifth, have a tough time proving that they have what it takes to overcome the odds and beat the incumbent. There are circumstances where there is no path to victory. In some cities you can be a horrible person who kicks puppies in your spare time, but if you have a D next to your name you will get reelected. In Philadelphia, on the very best of days, a Republican would get 25% of the vote. There are many instances of incumbents who have committed crimes staying in office or being reelected to office after a term in prison simply because their challengers could not appeal to the demographics of the district. Marion Barry comes to mind.
This is not to say you should not try. It is a warning to be realistic. Do the numbers add up? Go over how many votes the incumbent has won by in the past and the composition of the district. Do you have to get out your entire base, plus more than half the independents with a popular incumbent? Do the independents really vote independently or do they tend to vote for one party, but remain unaffiliated? These are important factors to consider before diving into a race, particularly as a challenger. If the numbers do work in your favor then the next step is to show that your candidacy has the components to be successful. High donations, early endorsements, volunteer support and positive media coverage are a few of the ways to show that you mean business.
If this is your first race, then many of these will come from your friends and family at the beginning. Gaining significant support, both financial and volunteer time, from your closest network shows that you have at least one set of people who believes that you have the capabilities to do the job. While it is sometimes stressful to rely on those personal relationships, if leveraged properly, over time the momentum will grow. Endorsements from friends and family will turn into endorsements from their networks until you don’t even recognize the volunteers at HQ anymore.
Make the endorsements count by putting a quote from a notable community leader on your literature if possible. Take every opportunity to demonstrate that your message is being well received by showcasing your events (make sure they are ones that have high attendance) and always have confidence. There’s nothing that makes an incumbent more nervous than a challenger with a good message and confidence in their inevitable success.