A few general tips:

Have the player with the fastest connection and the lowest ping to other players hosting the game (the player geographically in the "middle", if possible)
Disabling peer-to-peer will reduce the bandwidth needed on players who are not the host
Make sure the other players don ...

So i have two other friends who have just bought Factorio. We are using Hamachi for the connection and it works fine as longs as its only two players. They have quite fast internet and unfortunately i have quite slow internet. My friend with the faster internet hosts but as soon as the player count ...