If you're not going to be playing on a certain day, you should still spend your Mist Energy.

The easiest way to do this is to simply craft items.

Whether it's a 1, 2 or 3 star item, the Mist Energy doesn't cost anything to replace.

You can get ten 1 star items, so that's ten Haze bombs, for free. Ten chances of getting an epic Unique Variant and ten items you could potentially sell on the Bazaar for monies.

Or two 2 star items, so you could make two Autoguns, or two Caliburs. It would be best to combine them if you have neither.
So you could craft 5 Haze Bombs and 1 Calibur a day.
Or 1 Autogun and 1 Calibur.

You could also make 2 star armour as well, but the variants on armour aren't as beneficial. An Ultra bonus being only 25 points of defence, meaning it only really helps if it's in status effects.

I wouldn't recommend making one 3 star item a day, but the 3 star items might be worth it if you don't want to start a 2 star chain.

This is also a good way to get rid of those pesky low grade materials.

The Variants you would want to look for are:

Charge Time Reduction: Ultra and Increased Damage vs Jellies, Gremlins or Fiends.

For Caliburs and Autoguns, it may be a good idea to get Increased Attack Speed: Ultra. But it's less desirable than additional damage.

Desirable upgrade trees for good Variants:

Haze Bombs into Ash of Agni, if you have Trinket Slots, the Charge Time Reduction isn't that important.

Autoguns into either, Increased Damage for Gremlins should be Blitz Needle though (Gremlins are weak to piercing), Increased Damage for Jellies would be better off as a Volcanic Pepperbox, because Jellies are strong to Piercing and weak to Fire.

Caliburs should be turned into Cold Iron Carvers, for their additional Ultra bonus against Undeads. And they just look way cooler (pun?).

Corresponding items:

Trinkets are always helpful.

Focus Modules for the weapons in question are always a good idea.
Don't forget that weapons get an Ultra Reduction to Charging at level 5.
So it's less than ideal to have more than two bonuses.

The Fallen Set is just about the best set you can get, the Valkyrie Set is probably a little better rounded. The Fallen Set is also less than ideal with a Faust or Gran Faust.

But that's just about it.
Craft away, minions.