Alliance

Joining an alliance will increase the amount of support you can gain from other players in your endeavors.  A lonely player is an easy target, because the enemy alliance don't have to worry about diplomatic, they'll just eat your cities. But this doesn't mean that as soon you spawn you need to join an alliance, because this is wrong. Smart players make a good analysis of all surrounding alliances and choose the best one.

Position/Core 

Would you join an alliance far away from you?
Of course not, the support will take hours to arrive and the eney is next to you, if they help.
Would you join an alliance close to you, but spreaded over oceans?
No, if the alliance doesn't have a core, it will crumb. The most vunerable players are those in the borders of the alliance. Many of them will jump to another alliances and the members will do the same when they see the disbanding. If you're unlucky, you become food.
What's the importance of a core?
If every member of each other, they can support each other very fast and time attacks easily. Most of the top alliances start with a strong core with many islands full of blues(his members).

Members 

Another important factor of the surviving of an alliace is its core players(the most active and experienced players). They will sustain the whole alliance. Having such these players is a good indicator, but they must be close to each other. Otherwise, they can disband and things will get worst.
MRAs(Massive Recruitment Alliance) are often seen as bad alliances. Usually they get filled in the first days of BP, which is really bad. But if they have a good leadership, core players, good core, not spread over the oceans and there are no options left, then you should consider joining a MRA.

Leadership 

What makes  a good laeadership?
Diplomacy or Dictatorship, the leadership have to be active and experienced(core players). If they are "weak", member won't follow nor respect them. I'm not considering their personal abilities.
If a leader sent an invite, without even knowing you neither asking your objectives in the game, it just shows that he is probably an incompetent and will sink the alliance. Good leaders usually send formal messages of inviting or don't send.

Premades

It's common to find premades in the forums. Most of them ask for experienced players, but if you find a premade that accept beginners this can be a great start for you.
Even though, try to join the best premade, send a polite message and willing to learn. Good premades mention their structure, leadership, objectives and what kind of players they look.

Any doubts post in the comments.