I just graduated high school, have been into cycling (just finished first century ride last month) and try to take one to two 25 mile loop rides a week. On my way home, sometimes there is construction on the one road I take with bike lanes so I go a different way.

There is this intersection, 4 lane roads meet with left turn lanes from all directions. Not very pedestrian friendly as I think there are only cross walks going one way. I usually signal my way into traffic (which comes in waves) making my way into the left turn lane and then waiting in line.

However, there is a major railroad crossing right before the intersection. Being there is no shoulder towards the intersection and I am practically already taking the right lane, if there comes a train (which happens frequently) is it right to take the left lane before the crossing, wait, and then ride about 1/15th of a mile to the intersection?

Yes, get left early; it's easier than trying to merge into traffic later when it will be denser.

Ride in either the center of the lane or the left half of the lane when using the left lane on approach to a left turn. This discourages drivers from trying to pass on your left. If they don't want to wait they can make a lane change to the right to pass you.

I ride a short stretch of a 7-lane 45 mph road as part of my commute; I ride through two closely spaced signalized intersections before I get to my left turn. I get all the way left at or near the first intersection, ride through the second intersection in the left through lane, and then take my left after that. Waiting until after the second intersection to merge left means I may have a harder time merging left in the short amount of distance and time, depending on traffic and light phases. I've had no problems resulting from getting left early.

Always try to interact with traffic smoothly and do not wait to the last minute and try to force things. So yes getting left earlier is better then later.

Absolutely.