I think it is important to understand where the bruise comes from in relation to where it is when you see it.
For example, if your horse has a bruised sole you can be pretty certain that at some point in recent history there has been trauma to the solar corium.
I say 'recent history' because the time it takes for the bruise to reach the solar surface depends on:
Rate of wear/growth
It is not unusal for me to see a bruise, remove chalk and then it is gone. It all depends on how deep the bruise goes.
So for the moment let's focus on external trauma to the solar corium. This can be a short sharp shock, ie the horse trod on a stone. Or something more long term; overlaid bars causing corns for example.
But the chances of either type of trauma occuring can be reduced in the same way.
1 Maintain proper foot health
2 Feed the horse appropriately
3 Trim on when required (not seveal weeks late) and in accordance with natural principles
4 Treat your horse with respect and listen to them
For wall bruises I fear I may have to be a little more controversial - but only reflecting what I have seen.
There are broadly two types of wall bruise. One is the big purple/pink stain that is localised and typically seen in the quarters (moving towards the toe as the foot grows). This type of bruise is often seen in the shod white foot, not so much in bare, although it does occur in barefeet too. Sometimes, not always, this type of bruise is human/mechanical in origin. What I mean is this; the foot has been allowed to grow or has been trimmed into a (usually) boxy shape. The strain on the foot of this unnatural form causes trauma in the quarters, which then bruise. It won't be seen in dark feet (usually) because the bruise is covered by the horn pigment.
The second is the big purple ring that circles the whole hoof, in the same way as an event line. Again this is easily seen in pale hooves, but not those with pigment.
There are two main causes of the purple ring; dietary and mechanical and the latter falls into two further sub-divisions. When there is dietary stress the horse will throw an event line in its hooves. In extreme cases this will be bloody.
Mechanically, if the hoof wall is very weak it can fold under the weight of the horse near the bottom edge - for example when it is growing out a period of ill health. This will cause bruising, but it is only for a short time because the fold will be near the bottom of the foot and will soon grow out. The second mechanical cause I have seen is when a horse is shod 'aggressively' and the trauma to the foot will cause a bruise at the coronary band which will then grow down as a ring.
So if your horse is regularly getting bruises it is another indicator that somewhere, something is not quite perfect and you may need to rethink your horse's management.