Is it up to me?

[CalebTracker]

I imagine you want to avoid being a sort of "jack of all trades, master of none" at least in group play. While a healing ability might be great help for a damage dealer during solo questing, in group play players are expected to specialize rather than offheal as a damage dealer. Why? Because you offhealing means you are doing less damage, which is the reason you are in the party in the first place. So it is just more efficient to leave the role to the class that is most proficient at it. So I would suggest you pick a Job you like, and then focus on getting the cross-class abilities that help said job.

That being said, it doesn't seem you can really "ruin" your character. Level what you enjoy, and at worst you'll have to level some other class for the abilities you need for more competitive gameplay as well.

[Elysaine]

I only have 3 classes at the moment. Whitemage (Conjurer), Arcanist and Thaumaturge. Even if I had other classes already, I would only use cross class skills from these three classes. Because they benefit a caster class the most. My guess is if you solo on Archer and have Cure as backup spell it might help you out of a bind. But don't expect to be using it in a dungeon. As Archer you're a dps class, not a healer. So you wish to have abilities from other classes which will improve your DPS It's the other way around for a healer

Only DPS improving skill I've picked up on my Whitemage/Conjurer is the Thaumaturge's Thunder. It's a DoT spell. Increases your damage a bit, and I have never been frowned upon for using it next to Aero in a dungeon. Just to add some damage when not being required to heal at a moment

[Merryl]

I believe what your looking for is this http://www.ffxivguild.com/ff14-job-requirements-arr/
On that page you will find links to the classes that share cross skills and the job titles associated with them.
For archer your best choices would be THM for black mage, or if you want to keep archer skills on top chose pugilist for bard. Lancer also crosses with pugilist for dragoon.