This thread didn't make too much sense, but:

Use the middle ring [if triple] or small ring [if double], and pick a cog that lines up reasonably well.

Oh, and BMX cogs are <$5.

Small gears are the ****! Try starting with the middle ring, and a cog halfway down the cluster in back. That'll both give you a decent chainline, and a decent gear.

Do this:

[and don't forget to oil your chain!]