In a couple of recent threads I got to talking about optimization. But I didn't really explain my perspective on DFRPG optimization in general. That's what this thread is for.
Before I get into specific points, let me say this: there's no right level of optimization. But it's better if everyone is on a similar level. Otherwise the game can get imbalanced, and that can damage everyone's fun.
I'm going to be talking a lot about what you "should" do here. In this context, I'm assuming you're trying to strengthen your characters. If your group plays at a low optimization level, ignore me.
The contents of this thread will inevitably be limited and tilted by my own knowledge/ignorance and personal perspective. This is all just one person's opinion. Feel free to post your own thoughts on optimization.
General Principles
1. Specialize
If improving something you're good at costs the same amount as improving something you're bad at, improve the thing you're good at. Since you're good at it, you'll probably try to do it a lot. That'll give you more chances to use that improvement. For example, if you have a +1 spirit control specialization, a Refinement giving you +1 spirit power and control is better than one giving you +1 spirit and fire power. You'll cast more spirit spells than fire spells, so you'll use the spirit bonus more.
2. Avoid overlap
Being able to do the same thing in multiple ways is rarely an efficient use of resources. Superb Fists and Superb Weapons are both fine, but having both is not as good as having either and Superb Rapport. Combine this with the first principle and you'll get a character who's great at multiple mostly-unrelated things, so they can be effective in a wide variety of situations.
3. Don't make statements
Aspects are great for defining who your character is. Powers, Stunts, and Skills are somewhat less so. I've often seen people take No Pain No Gain on characters who have little mechanical use for it to show that those characters are tough and can endure pain. That's a fine statement to make, but there's no need to waste a Refresh point on it. An Aspect would make the point better, and be more efficient optimization-wise. And if you really want to make it mechanically relevant, you can express the same statement with another Stunt/Power that suits your character better.
4. Buy carefully
Just think before you put anything on your sheet. Ask yourself: does this make my character stronger? And if you can't say yes, don't take it. This is especially true for Stunts, since it's very easy to waste a ton of Refresh on semi-useful Stunts.
On Skills
1. Make sure they match your powers
Many Powers require Skills to work. Someone with Evocation and no Discipline to speak of is not getting much value for their Refresh. Same goes for someone with no Might, Fists, or Weapons who takes Supernatural Strength. So if one of your Powers won't work well without it, make sure it's near the top of your pyramid.
2. Raise the ones you expect to roll a lot
The value of a +1 bonus to a Skill depends on how many rolls it'll increase and how important those rolls are. Chances are you'll get into a fair number of conflicts, so whatever Skill you use to defend will be valuable to you. And whatever Skill you use to attack/block/maneuver will be too. Make sure they're both solid.
3. Keep an eye on your stress tracks
Average Skills are cheap, and that third stress box is really nice to have. The fourth is good too, so if you can spare a Good Skill it's often worth it. But an extra mild consequence is a bit less exciting, since it's taggable and getting it costs you a Superb Skill slot. I usually prefer to have 1 or 3 in each stress Skill unless the character has a Power or concept that makes them likely to actually roll their stress Skills on a fairly regular basis.
On Stunts
1. Don't stick to the Your Story list
Your Story tells you that its list is not comprehensive, and that you should make your own Stunts. Listen to it. Stunts that you invent yourself will be exactly what you need, unlike ones you pick from a list. And a character whose stunts fit perfectly is noticeably stronger than one whose stunts don't.
2. Focus on high Skills
There's no point giving yourself +2 to some part of an Average Skill when you could just move that part of that Skill to a Superb Skill. And as I said before, specialization is a good idea. With a few rare exceptions, you should probably stick to your best three or four Skills when buying Stunts. As an added extra, this often makes characters make more sense. After all, your high skills are generally the ones that define your concept.
3. A stunt should improve a speciality, add a capability, or cover a weakness
A single carefully-chosen stunt can add a whole new area of competence to a character by expanding an apex Skill or giving a unique effect, make that character Epic/Fantastic at something they would normally be Superb/Great at, or remove a significant weakness by letting an apex Skill address it. These are all very powerful things, and chances are they're better than anything else you can do with a Stunt.
On Powers
1. Rebates are abusable
The rebate Powers in Your Story all give linear rebates. Attach them to the minimum number of Powers and they'll give you much more Refresh than the trouble they cause justifies. For example, you can get Mythic Toughness for 1 Refresh: take Excalibur's Scabbard, which is an obvious item for a +2 rebate. It protects you from injury but not from suffocation, so there's a +3 Catch. So now you have flavourful, mythically-accurate Mythic Toughness for 1 Refresh. This isn't very fair, so please exercise restraint with rebates.
2. Not all Powers are created equal
Most Powers are useful and worth taking, but there are some to avoid. Bless This House, Pack Instincts, Breath Weapon, Mana Static, and Tattoos of St. Giles are all pretty weak. Feeding Dependency and Demonic Co-Pilot are huge pains in the neck, unless you're abusing Feeding Dependency by putting it on like 2 Refresh of stuff. Wings is better than Spider Climb. Evocation specializations and foci are significantly better than Thaumaturgy ones once you've hit the magic number of 5 control to guarantee controlling 1 shift at a time.
3. Have a plan
Make sure your powers fit together properly. Don't take Inhuman Strength and Channelling (Fire). Have a goal in mind, and build towards it. This is easy for some Templates like the Wizard, which have a good plan built in. It's not so easy for some Templates like the White Court Vampire, which inherently pull in multiple directions at once.
Anyway, I hope this is useful or interesting to y'all. Feedback and input are welcome.