I haven't overclocked since the Core 2 Duo days. I had an E6850 up there, I think 3.8 Ghz. I had a Pentium D 820 up around 3.4 Ghz before that. That PD 820 was a pair of 90W dies, so that got me into water cooling.
Pretty much everyone has chimed in with the important stuff already. A quality stable board from a reliable manufacturer that supports overclocking, I'm an Asus fan personally, but I've used all the major players and then some over the years. A good power supply, that can support your efforts. Finally, cooling! I wouldn't waste much time on air cooling, with the plethora of AIO coolers on the market now, pick something off the Corsair, or Coolermaster AIO cooler tree, and use some good thermal paste. I was an Arctic Silver fan forever, but have gone to Thermal Grizzly Kryonaut within the last couple years.
A lot of new boards have GUIs that will basically OC the system for you, directly from the Windows desktop, a lot easier than it used to be.
Back in my day, you adjusted your clock multiplier and/or voltages, ran a stress test, rinse and repeat, until it BSODed, then backed it off a touch.
Personally, I don't think I'd put a lot of effort into OCing an A8, you can pick up a same gen A10 5800K for $45, that should work in the same MB (might need a BIOS update) and will give you more gains than you'll get out of OCing that A8.
I'd probably spend $150-$200 on a some new-ish or eBay sourced parts, MB, some DDR4 RAM, and a 7th or 8th gen i5.
I've had great luck shopping 2-3 year old hardware on eBay. I have great luck with the "make an offer" option on eBay listings too. Worst they can say is no, but they usually counter with something reasonable.
Good luck!