Race: When to skip zones?

So, from my understanding, to push higher in the race, it is good to know when to skip a zone, or when to leave a zone, or when to farm a zone for xp because it is good for xp. So my question is, what zones do I do this with? I am seeing people able to stay at least a few lvls ahead of me on short races (more on longer races) that lets me know, I am not keeping up. Any tips I can get with this?

I think it's more about the zone levels and your level relative to them. Google the colored zone/xp chart.

Try to always be underlevelled by 3-4 levels so that you are getting 100% xp with the largest possible underlevelled gap. This way you are killing mobs that give the most xp while also getting 100% xp.