Depends on which kind of bows you like to use, really. Any set that offers Focus, X Shot Type Up, and something like Evade or Attack Up will generally do you well. I'd recommend staying away from Load Up though, since it's not nearly as good a DPS skill as people think.
I use Scatter bows, and I normally use one of 2 sets:
Zinogre Z
Kushala X
Black Belt Guards
Kushala X
Kushala X
Charm (Pellet Up+5): This gives Evade+2, Heat Cancel, Focus, Pellet Up and Power C Add - Great for the Ceadeus and Gold Rath bows. Power C add is completely gemmed in too, so you could remove that and go for a different skill if you like. Also looks RIDICULOUSLY good for a mixed set.
Kushala X
Zinogre X
Duramboros X
Kushala X
Kushala X
Charm (Attack+6 OOO) Gives Attack Up XL, Evasion+1, Pellet Up and Focus, which is a great general purpose set too. In this set, Pellet Up is totally gemmed in as well, so you can replace that with any skill of equal value. It does require at least 2 weapon slots though, unless you have a better charm.
Finally, there's a set kicking around that works really well for the Seregios and Akantor Bows - I don't have access to Athena's Armor Set Search at the moment, but you can get Ruthlessness (Weakness Exploit+Critical Eye 2), Focus, Load Up, and Rapid Up with a half decent FastCharge charm. One of the few cases where Load Up is actually really helpful ^^