In a society dominated by powerful guilds and a world where the greatest challenges must be faced by large groups of highly co-ordinated and well-prepared heroes, what is required of the serious solo adventurer?
Reputation. Without an illustrious guild name over your head, your personal reputation is key. All the principles of courtesy to others, fair play, knowing your class/build and preparedness go double for the person whose invites stand on their own reputation alone. If you aspire only to be a well-geared delinquent, you will find an appropriate guild on your server to do that and get away with it. Solo play is not recommended for ninjas or unreliable people.
Friendships. This goes hand in hand with the above point. Know your key allies and cultivate mutually beneficial relationships.
Determination. Whilst enjoying all the freedom in the world, you must also do without scheduled guild runs. Therefore you must persevere to use your time wisely and pick the best opportunities for development. People pug for all kinds of reasons, and the poor quality of random groups is exaggerated in popular talk. However, you will have to accept that at least part of the time the groups you join will fall apart. On the bright side you set your own timetable.
Pride. At the end of the day you did it your way. Your success or failure will depend not only on your keyboard skills, but navigating relationships and choosing opportunities.