In general, and just talking about Cardiff, we can make a fair guess at which a/c are going to want which runway, approaches from the south and east have less track miles for 30, from the north and west less for 12.
If the wind is calm, say 5 knots or less, when I see an estimate time coming up for an inbound I will normally phone approach and tell them that both ends are available ( obviously dependent upon traffic). Then with phraseology something like " Runway 30 in use, 12 is available, surfice wind xxx @ 5 report your intentions." the pilot will either say 12 or 30. We have tied it up so all that is left is to switch the ILS and Lights.
A pilot may request it in which case, APR call TWR and then make a decision based on traffic. Ultimately, it is the tower controllers responsibility to say yes or no, but with a lot of co-ordination from the approach man / lady.
A similkar process for departures as well.
Personally, I will always use the most into wind runway, if the surface wind goes round in circles then the forecast 3000' wind or a 1000' wind check from an inbound to help decide. Any aircraft who wants to land or taxi to the In use runway takes priority over any aircraft positioning for the out of use runway. (Unless in an emergency situation).
Hope that helps
TIO