This is a common trick used by veteran players of Harvest Moon and Rune Factory but it may be useful to post it here for beginners. The information is included in my Rune Factory Frontier Guides by the way.
You can raise your Skills with respect to a particular type of weapon or tool simply by equipping it and swinging it. In Rune Factory Frontier, there are two times during the day/night when this can be done with the greatest benefit and least sacrifice of valuable energy or time.
Remember that time does not pass whenever your character enters a building. You therefore can use any Weapon or Tool inside your own Farmhouse or in any other building while time stands still. Energy, however, WILL be used.
The two best opportunities to increase Weapons and Tools Skill Levels in this way are whenever you go to the Laga Springs Bathhouse and whenever you return to your Farmhouse at the very end of your day.
Whenever your character take a Bath at the Laga Springs Bathhouse, all Energy is restored and both Health and RP bars are refilled. It therefore is wasteful for your character ever to leap into the bath before he has used almost ALL of his HP and RP. To do this, equip any Tool or Weapon and use it in the Bathhouse until your energy reaches the flashing red indication that respresents dangerously low levels.
Remember that every Tool has its own specific Skill and that Weapons and Magic are two different skills as well. Often a player will focus on one to the exclusion of the other in combat situations... if so, equip the type of Weapon in which your Skill Levels are lowest whenever you go to the Laga Springs Bathhouse or return to your Farmhouse at the end of the day.
When all your chores and tasks are completed and you are ready to leap into bed, do not do so without expending whatever excess energy remains. Remember, however, that you need to go to bed before 1.00 a.m. if you wish to awaken at 6.00 a.m. with both HP and RP fully replenished. Provided you go to bed before 1.00 a.m., you can use your energy to the point where the red flashing indication is displayed and still awaken in good health at 6.00 a.m.
If you employ this strategy on a daily basis, increasing skill levels that otherwise are not used sufficiently, you will be able to increase ALL Skill Levels to maximum without any difficulty.