Query-time boosts allow one to specify which terms/clauses are "more important". The higher the boost factor, the more relevant the term will be, and therefore the higher the corresponding document scores.
A typical boosting technique is assigning higher boosts to title matches than to body content matches:
(title:foo OR title:bar)^1.5 (body:foo OR body:bar)
You should carefully examine explain output to determine the appropriate boost weights.