TL;DR -- Don't swap out your current dwellers until you have replacements for them.
I am not sure this is a 'current' method but the one that makes sense to me. First up though is expand slowly. When you add new people, especially a baby boom, it can be unmanageable (My second vault I actually birthed 0 children simply to avoid this.. 1-2 people a day from the radio is fast enough growth for me). But this is the flow I use:
- First fill up the rooms as best you can for their stats. Remember that Luck universally helps any room so take that into consideration.
- When I get training rooms new people go into them. Now I am a bit compulsive here and force all new people to max out every stat, if you are focusing on a specific one for room production then just remember as above, Luck counts towards all rooms.
- When I have a trained up vault dweller I will swap them into the room where they belong and the person will come out of the production room and enter training themselves.
The end goal is that your initial dwellers are the ones who end up being the ones sent out to bring back gear. You can train people up to send them out later but I think this is the part that you really wanted out of the flow.. Replace the initial people with better trained people. The replaced people get trained up to awesome levels of skill to go out and gather gear for you.
Now, a little side note that I have discovered.. When people level they get their health back. This goes for wanderers as well. You can take a level 1 person and train all of their stats up to max and send them to the wasteland for an -extremely- long time. Because they will level from 1-50 if properly geared (ie your best gear) and so can do runs that are days long because they will mostly heal up by leveling.
Anywho, this flow will allow you to avoid having 'wasted' people as you are aiming to get a fair number of wanderers in the end.