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Boiling water is the simplest first step and works for grease and soap buildup in kitchen sinks. Pour a full kettle slowly in 2–3 stages (letting it work between pours). Caution: don't use boiling water on PVC pipes — use very hot tap water instead. Don't use boiling water if there's standing water that won't drain, as it can splash back.
A plunger is your most powerful tool for complete blockages. For sinks and tubs, use a cup plunger (the simple dome shape). For toilets, use a flange plunger. Critical technique: block the overflow opening (the small hole near the top of a sink bowl) with a wet rag before plunging — this creates the suction you need. Plunge vigorously 10–15 times, then check if water drains.
Baking soda and vinegar is a popular home remedy, but it's more useful for maintenance and mild buildup than for serious clogs. Pour 1/2 cup baking soda down the drain, followed immediately by 1/2 cup white vinegar. The fizzing reaction can break up loose gunk. Wait 15 minutes, then flush with the hottest water from your tap.
For bathroom sink and tub hair clogs — the most common drain problem — the Zip-It drain cleaning tool is the best solution. It's a flexible plastic strip with barbs that costs $3–5 at any hardware store. Insert it into the drain, rotate as you push down, then pull out. The hair wraps around the barbs and comes out with the tool. More effective than any chemical product.
Avoid using chemical drain openers like Drano regularly. They're corrosive — they'll damage older metal pipes and degrade PVC pipe glue over time. They also heat up significantly during the chemical reaction, which can warp PVC. Use them as a last resort before calling a plumber, not as a regular maintenance product. If none of the DIY methods work, a plumber's drain snake (auger) is the professional solution.