Training facilities

[Suicide Junkie]

Training facilities are absolutely critical in multiplayer games.
If you don't train, you are giving the enemy a total of 40% to-hit bonus in battle.

I reccommend building them at your primary spaceyard sectors. Ships will start getting trained as soon as they're built or unmothballed, and you don't have to shuffle ships around.
If you are a Psychic race, build them in your border systems so your ships can train while defending warppoints.

Take note that when ships are mothballed the crew leaves and you lose all ship experience. You will need to retrain after unmothballing.