Part of the reason why First and Business Class seats are at the front of the aircraft is that this allows these premium passengers to be among the first people to leave the plane.  This then allows them to be ahead of the rest of the plane at the immigration lines and to pick up their baggage and proceed through customs first.

You may have seen the flight attendants stand in the aisle or close the curtain to allow all First and Business Class passengers to leave the plane before a single Economy passenger is allowed to leave.  There is a little known secret that allows any Economy passenger to be among the first people to leave the plane.

Wait till about half way through the flight, when the food and drinks service is over and when the flight attendants are less busy.  You want to let them you know have an urgent reason to leave the plane as soon as you land.  The most common reason would be a short connection to another flight, perhaps with another airline.  Equally as important could be a meeting that you are in a rush to get to, or some other event such as a wedding.  Anything that legitimately means you have a need for some priority in leaving.

If there is space, you will be relocated towards a seat at the front on the plane about 30 minutes before landing.  This means that you get to sit in a First or Business Class seat for this time as well – which is a benefit in its own right.

On international flights, First and Business Class passengers often get Priority Immigration passes.  These allow you to use special immigration lines that are usually shorter than the regular lines.  Most major international airports have this and it can save a considerable amount of time at passport control.  It is worth asking for one of these, whether or not there is space at the front of the plane for you to sit before landing.