I think the best way to explain moghancements is that each furnishing has:
A) Element with corresponding moghancement
B) Strength
Beds are a little bit different, because they all have different elements, but all give moghancement experience.
Mysterytour has a nice page with all the furnishings listed with their strengths.
http://mysterytour.web.infoseek.co.jp/ffxi/us/tips/moghancements/moghancements.htm
So for example, if I put a Bronze bed (strength 6) in my mog house with a Porcelain flowerpot (strength 2), the bed will override the flowerpot and I will get the experience enhancement.
If however, I put a Bronze bed (6) in my mog house with a Maple table (strength 8), the table will override the bed and I will get the gardening enhancement.
It gets more complicated when you have more furnishings involved, but this is the basic idea behind moghancements.
If you want to get an enhancement to be stronger, you have to buff it with furnishings that have that element.
For example, if I wanted the fishing enhancement to be very strong, I'd put an Armoire (strength 16, water element) in my mog house and then buy tons of armor boxes and put them in my mog house to increase the strength of my fishing moghancement.
I'm not 100% sure on this so correct me if I'm wrong but I think there are 3 different strengths you can achieve, and your mog will tell you a different thing for each strength.
Hope that helps ^^
Edited, Wed Nov 3 17:44:33 2004 by Apocpink