It is posible to set priority on properties/fields?
I want that a document/page with a hit in the property "Heading" would be rated higher than a document with a hit in the property "MainBody"
Yes you can here is a simple example where the importance is higher for hits in Author then in the other field, content, I am searching on :
client.Search<BlogPost>() .For("cyklade") .InField(x => x.Content).AndInField(x => x.Author,4).WithHighlight(x => x.Content).GetResult();
You can read more about searching in the documentation at http://find.episerver.com/Documentation
Hope that helps.
Even if you don't set boosting on field you often will get a "natural" boost since the the number of terms in heading are less than in the main body.