I am making an I/L mage and I have no idea of the sort of skill build I should be following. Any suggestions or links to guides? There are no IL guides on this forum.
http://www.hidden-street.net/forum/threads/11215-The-Canadian-Quality-Guide-to-Mages-Page-1-w00t-! <- a possibility. For 2nd job, the lightning first build is superior. For third, I'd ask an I/L what they recommend maxing (seal or not, booster or not) and for 4th you pave your own path.
3rd job definitely max booster, seal/slow is really up to the player. But seal is more useful since you already freeze things. Slow is useful for paps 2nd body and seal for newts grinding. But either way to won't need either that much. As far as Thunder Spear vs Comp, Conp has the better DPS but TS looks cooler IMO.