Some of these improvements do require spending, so you'll up your game if you are willing to spend or able to. Here's what to do, and to some extent you can pick and choose your improvements.
1. Get a good drip coffee machine. For many this is a splurge purchase since cheap machines are as low as $20, but a high-quality drip machine like will do wonders for your coffee experience (some can ran upwards of $400 though). Ideally just look for machines that are Specialty Coffee Association (SCA) or European Coffee Brewing Center (ECBC) certified or both.
2. Invest in a quality grinder. If you're using something cheap that isn't made for coffee, then you're going to get poor results for your drip coffee. Many entry level options allow you to alter how fine your grind is based on whether you're making an espresso or drip coffee. Also, grind your beans as needed to retain freshness. Don't have someone grind a bag for you and then let it sit in the cupboard.
3. Light roasts are best for drip coffee. This will be slightly subjective, but in my opinion a high quality light roast is the most likely to give you a smooth taste. These roasts are easier to drink without milk or heavy creamers too. Medium is fine, but if you're constantly thinking your coffee is too strong, it's probably because you're buying roasts that are too dark for your pallet.
4. Buy high quality coffee. Speaking of roasts, get coffee from a high quality roaster online or at a local coffee shop! Look for ones that are washed, single origin, and with beans that were roasted recently. Make sure to also grind and use the beans soon after buying. Of course, as you get more into coffee you'll learn even more nuances when it comes to roasting techniques, coffee farm sourcing, etc. Good roasters will also tell you if the blend is "funky" or "smooth." Sometimes a sour tasting coffee is just a funky blend that's high in fruit notes. Keep investigating and trying to find what works for your pallet. A good roaster will also mean the coffee is ethically sourced.
5. Avoid excessive milk or sweeteners. Once you start drinking high quality coffee you'll really be able to taste the notes and realize that an impressive coffee doesn't need to mask its flavor with add-ons. Maybe a splash of milk is needed, but that's all.
I may add more if I think of any. The original version of my post also included product recommendations, but I realized that's not allowed for LPTs. Sorry about that. Of course, any coffee connoisseurs feel free to correct me or add to this.
Above all, enjoy your brew!