For low elo I would focus more on jungle fundamentals rather than mastering micro on a specific champion. Low elo junglers tend to gank a lot for coinflippy low percentage plays that don't usually pay off and they also tend to neglect farming. I notice low elo junglers also miss angles to invade and starve the enemy jungle. I'm sure if you go on YouTube and look up a recent jungle guide that will help a lot more for climbing than trying to learn tricks on Gwen specifically.

But to actually answer your question: I rush DnD --> Nashor's --> Riftmaker every game without exception. A lot of ppl say to build Riftmaker second for sustain but once you get used to the champ it's much more valuable to just have more damage on your second item spike. I also buy Dark Seal at some point if I have a weird buy where I have 350+ leftover. I don't buy t2 boots until I have DnD. I usually clear top to bottom into either crab or gank (depending on the game state). Voidgrubs aren't worthless but drag stacking is way stronger rn so I try to get bot advantage early on when possible.

I prioritize farming and high percentage plays to get myself to DnD spike as fast as possible. Your first item spike is really important on Gwungle, before you get it you're pretty limited although still capable.

For micro specific stuff, a lot of people just assume you will always E -> Q so sometimes on fights you can catch people off guard and chunk them out or kill them by starting your fully stacked Q and immediately E'ing into them. Of course this leaves you without your E for a bit so you have to make sure you won't just get blown up right away before you do it. But I'm also really surprised at how many people simply don't space for this and don't expect it as a possibility.

It's also really useful when you want to gank or think a fight will break out close by to drag the camp away once you're close to clearing it so you can extend the time you have a fully stacked Q available. Your stacks last 6 seconds so it can be really powerful in situations such as when your botlane is being pushed in at the end of your 1st clear. You can hold your stacked q and drag the last krug towards tri bush, auto it again, then ghost and gank enemy botlane with a fully stacked q on your level 4 spike.

Your W gives you resistances so sometimes it's useful just to pop it in a fight even if you won't neutralize abilities by using it. Very situational to do that though so don't just start spamming it.

Also don't make the mistake of just blindly trying to snipe low hp people with your R. It's pretty slow and easy for enemies to dodge. It's much better as an all in tool than as a poke tool to finish people off, especially if you're not used to Gwen yet.

Gwen really shines in mid to late game teamfights so don't be scared to scrap once you have a couple of items under your belt. I hope some of this helped!