I am fairly new to enchanting so forgive me if this is a stupid question...
Does it matter when a glyph is applied to an item, as in before or after improvement?
It shouldn't matter when you add the glyph because the improvement should only affect the item's values so Armour, weapon damage and any added traits and not the add on enchantment values but I have never tested it so I can't confirm it.
PUG Life - the true test of your skill
18 characters, 17 max level, at least 1 Stam and 1 Mag of every class, 1 of every race and 1200+ CP
Tanked to Undaunted 9+ Mag and Stam of every class using Group Finder for 90+% of the Vet Dungeon runs
It does not matter. The stats of the glyph will automatically scale with the improvement materials, especially if the trait is infused because the percent of enchantment effectiveness this trait gives will increase with each improvement tier. You can do the enchantment first or the improvement first. The end product will be the same.
The "Infused" trait on armor that makes enchantments more powerful can be improved, but not the enchantment itself. So a White item with a +100 Health enchantment might become a Gold item with a +115 Health enchantment. But it was the Infused trait being improved, not the underlying enchantment. If you had waited until the end to apply the enchantment, it would still give you +115 because the Gold item is "more infused".
If you have any trait other than Infused (Impenetrable, Reinforced, Divines, etc.) on the item, the enchant should never change. It if was +100 Health at White, it will still be +100 Health at Gold.