I'd recommend reading this
http://wiki.project1999.com/Thrasos'_Bard_Guide
If you are grouping and don't always have mez, charm, selos (if outdoors) snare/slow up, you're doing it wrong. A good bard saves live, and you always want your CC songs up for when they are needed. My normal song slots are:
(1) swap
(2) swap
(3) snare/slow
(4) hp/mana regen
(5) swap
(6) mez
(7) charm
(8) selos
For my standard combat twist, I go 1-4. 5-8 are for utility or CC. So if i was pulling, 5 would probably be lull, and I would probably also use cancel magic to tag. Since bards normally pull indoors at 40+, I would put cancel magic in slot 8 where selos normally goes.