Best way to use EXP Boost In Guild Wars 2?

Best thing you can do is using the exp boosters in lvl 80 areals and do make events, where either alot of enemies spawns, or go to places, where max level enemies are, which haven’t been killed since ages, because so longer a monster hasn’t been kille,d so bigger rises its bonus exp, which scales also up with the exp booster.

ALso use both exp boosters, those from the shop (+50) plus those green ones for laurels to maximaise your exp income and use the kill streaks for massive additionasl +100% exp, when you are sure, that you can kill alot of enemies in short time (30 seconds per kill, so take some friends with you and play with alot of AoE Damage to go sure, that you hit as many enemies as possible so that you collect as many exp from all the hitted enemies)

I didn’t even use all of that, just the normal exp boost and got with that alone in areas where enemies haven’t been killed a long time ago like 2000 Exp per Kill.
In an hour killing stuff in an empty map sums up a nice amount of exp.Also theres the birthday present for another +100% exp, so if you have that, use it naturally for 24 hours more exp.

The best thing in general to level fast from 1-80 is exploring, hearts, personal story and events with exp boosts for the kills with a group, so that you can do all the stuff quicker.
From Level 30 on, you could do also Dungeons, when your Group Members are all 80, they can pull you through Story and Explo quickly. Every Explo Dungeon Run is basically a guaranteed Level Up.

So just find some people, that clear for you at 4 people the way in Ascalon and you could do that too, if you find exploring, personal story, events ect. is to slow.