The bard's skill in music makes it a very unique class, as it is virtually impossible for any character without the skill to use charming, which the strategy of the bard is centered around. While playing the lute of charming the bard will mesmerize enemies. You can then disarm them (if their weapons are not cursed) and free them from mesmerization, and attack them. This controlled combat makes bards an excellent class to gain skills many different types of weapons.
If you feed a mesmerized monster, it will turn into a pet. Only some pets (felines, canines, and humanoids, mostly) will remain your pet forever, and others will turn against you after some time. Felines, canines, and humanoids generally make the best pets because felines and canines can Identify curses and humanoids can wear most equipment. It is better to get pets in the mid-to-late section of the game because early monsters are weak and almost guaranteed to not make it to the lower levels. You do not want to have too many pets (or mesmerized "minions") because they will take all of your experience.
"Tell a story" is a very powerful skill, because it stops all enemies from attacking (but be careful with your pets and minions—if you let them attack the monsters, they'll spring back into consciousness). Use it in a tight spot, and then mesmerize the frozen enemies, or run away/prepare yourself to attack them from a distance.
Because of the power of the lute and "tell a story," and his capability as a handheld weaponeer or a spell-caster, bard is one of the most powerful classes and easy classes in the game (though his early game is very slow).
Bardesses' harp makes weapon skill go up insanely fast. You'll want to use the h/j/k equipment selection keys. Set up one key that's your harp, h, and one that's the biggest weapon you can find for killing, k. Put the monster to sleep by playing the harp. Hit k, attack, and you will suprise attack the monster, which does double damage, ups your skill and always hits.