Either have a friend help you get all 8 Ascendancy points right away, pay someone Divs to do it, or find one of the many people in general offering to do it for free.
Important note: if the person advertising free Ascendancy runs has a completely nonsense name (think: Plnsuf, Axcetlp, etc.) they are almost certainly a scammer who is going to tell you that you just need to join their Discord and "register" for a run. Look for people whose names aren't just a random string of letters for an infinitely higher chance that they're legit.
You've gotten some great advice on good twink gear, but don't forget that Tier V support gems have no level requirement, and you can get Perfect Jeweler's Orbs super cheaply this season. It's pretty crazy how big a boost 5 support gems in your main skill is when you're level ~30.
When I'm speeding through the campaign and I enter a new zone, I like to also find the exits to all of the adjacent zones and tag the waypoints there real quick too. You definitely need to be careful that the instance of the original map you're on doesn't reset due to you not going into it for ~10+ minutes, but it always saves me a bunch of time, especially in Act 3 where zones are giant and it can legitimately take a while to find each exit if you've gotta uncover the instance map again each time.
Lastly, and this might not apply to you, but the biggest time waster for me when I'm trying to blast through the campaign is just my natural impulse to do/see/find everything. On the overworld map, you'll see the points of interest for each zone - absolutely take the time to do the stuff that rewards you permanent buffs, but don't be like me and decide you'll, "just find the Troubled Camp/Gilded Beetle/whatever real quick, because how long could it really take?" because the reality is, it'll take longer than you think, and all those little ~15 minute diversions add up.
Keep your eyes on the prize, and just crank through, because you've got a seriously awesome reward (a kick ass, crazy-strong build) waiting for you at the finish line.
Good luck!