This would basically be adding a level of Weapon Focus with a given weapon, meaning a total +2 to hit and damrolls with the focused weapon, prerequisite, weapon focus with the weapon in question.
I am proposing this specifically for the use of prestige classes, and not for publicly accessible trainers. One repeating trend I see within many prestige classes, especially those that require focus with a weapon, at some point along the progression either offer improved focus by name, or some other special class skill which equates to it.
Improved Weapon Focus - Prestige feat
Improved Weapon Focus - Prestige feat
"There is no safety for honest men except by believing all possible evil of evil men."
Kregor - Ranger of Tangled Trees
Rozor - Lady Luck's Duelist
Tygen - Ranger-Bard of Mielikki
Kregor - Ranger of Tangled Trees
Rozor - Lady Luck's Duelist
Tygen - Ranger-Bard of Mielikki