I personally try to do what I can when I can. I am a little lazy in the fact that I try to get people who are either indifferent, or even apathetic gun owners to get more involved, and try to teach new skills and aspects of shooting. People that are straight up anti, well I fight the good fight, and politely argue any points they bring up. I use the data from gunfacts.info as the basis for most of my arguments, but I get a little tired of the name calling, and anger directed twards me after the eventual breakdown of their logic.
They must be aware of the opportunity to own guns.
most people know they could own a gun, but usually know little about the process, or what can be owned. Several people at the range comment on how they would like an AR or AK like I have, but think they are illegal, or that I must be a cop to be allowed to have a dreaded "assault weapon". I let them try it, and after people normally comment on how comfortable and easy it is to fire and FUN, I tell them that they have the right to own them, as they are just modern and versatile weapons, no more, no less, but are a common target of people who work to ban guns. With the same 4 peices of paperwork as it takes to buy a pistol (in MD) they too can own one, a couple people have taken my advice.
They must perceive gun ownership as a benefit to themselves
I try to pursuade to the fact that a firearm is a unique and wonderful tool. One that can protect your home and your family in the event of a national disaster, or common robbery. Can give people of all ages hours of fun at the range. A firearm can introduce you to new people with common interest, and social events like a competition, or group hunt. They can help improve concentration, reduce stress, quicken hand eye coordination, and provide several levels of excercise.
They must have an opportunity to try shooting
this is an easy one, invite a coworker, neighbor, friends, or family to the range. New shooters can be very excited about it, and tell others, who may be more willing to try shooting with another new shooter, than someone who has shot for years, because they may be afraid of looking bad. Many shooters and clubs can be kind of secretive, and closed off to those who may have an interest, while it may keep away newbies who may not know all of the subtle courtesies, it can hurt the cause. We should be a public and open group, hide your rights and they will get legislated away.
They must view owning guns as more beneficial than borrowing or renting them
Someone may want to rent or borrow a gun to find one they like, and that is fine, but if you were to need it when something goes bump in the night, having a rented gun locked up at the range does you no good. And much like people who own a bowling ball, or golf clubs, your own gun gives you a consistent platform to learn, and gauge improvement with a farmiliar feel.
They must understand the threats to their continued gun ownership
This is something best approached delicately, but decisively. I normally move people up from a 22 (which I have any new shooter try first) to an AR. It is a light recoiling easy to fire weapon, and everyone that has tried it loves it, this is where I fill them in on the truth about it's abilities, and what the media and politicians CLAIM it can do, and therefore propose to ban it. I point out that hunting is a sport in its own right, and a tradition, but some people just prefer to shoot at paper or steel, and they have no less of a right to own firearms than someone who hunts. The wheels start turning the next time some politician is on TV saying he is a lifelong hunter, but AWs should be banned, coupled with a few statistics the hypocrocy, stupidity and true agenda of gun control is exposed.
They must have a way to counter those threats by personal action
One simple thing is to encourage gun owners, and those sympathetic to the RKBA to vote accordingly, but the fact is that very few people are needed to steer the direction of policy and laws on a day to day basis. One person, who joins a pro RKBA association, votes, and writes a few letters a year to representatives and media sources can be viewed as representing thousands, and therefore has more say in what laws are passed than someone who simply watches what happens and shakes their head. I have encouraged about a dozen people in the last year to join the NRA, and given about a dozen more memberships as gifts to apathetic gun owners. Lots of gun owners have a bone to pick with the NRA, but they can help to show exactly what is rolling through national and state legislatures, and give instructions as to what can be done about it. The more exposure one has as to what is going on, the more they tend to rationalize the issues and understand the injustice that is gun control.
I appolagise my reply is a little lengthy, but this is my perspective as a pro RKBA activist, and what has worked for me in furthering the cause, i hope that if we can borrow tips and ideas from each others experiences there can be no-one that cannot be pursuaded to at least objectively and logically look at the issue, and once objectivity and logic are applied we have basically won as the genius of the 2nd ammendment, and the wisdom inherent of an armed populous can not be ignored.