Renter-friendly home repairs you can do yourself
Plenty of small problems in a rental don't need to wait for the landlord: a running toilet, a slow drain, a chirping smoke alarm, a squeaky door. These fixes don't change the place, need no permanent parts, and are the kind most leases expect you to handle. Anything bigger, or anything that involves gas, wiring or water damage, belongs with your landlord.

Before you start, check two things: what your lease says about repairs, and whether the problem is really yours to fix. Most leases expect tenants to handle small upkeep, like a flapper, a clogged drain or a smoke alarm battery, and leave anything involving the building's systems to the landlord. If you're not sure, a quick text with a photo usually settles it.
Keep the old parts and your receipts, and put things back the way you found them. That's also your best protection at move-out, when a patched nail hole and a fixed running toilet look a lot better than a list of problems nobody reported.

Guides in this list
Carbon monoxide alarm beeping? What it means

Change your HVAC air filter

Circuit breaker keeps tripping

Clean clogged dishwasher spray arms

Clean dirty grout without harsh chemicals

Clean your refrigerator coils

Condensation on the inside of windows

Dishwasher not cleaning dishes

Dishwasher not draining

Door swings open or closed on its own

Find your main water shutoff

Fix a crooked or sagging cabinet door

Fix a loose towel bar

Fix a loose, wobbly toilet seat

Fix a running toilet

Fix a squeaky door hinge

Fix a sticking deadbolt or door lock

Fix a sticking wooden drawer

Fix a toilet that won't flush all the way

Fix a window that sticks or won't open

Fix low shower water pressure

Fix low water pressure at one faucet

Fix stripped door hinge screws

Get rid of a smelly washing machine

Hang heavy pictures and mirrors safely

Hang something on a plaster wall without cracking it

How to find a wall stud (with or without a stud finder)

Ice maker not making ice

Mold or mildew on the bathroom ceiling

Refrigerator not cooling

Repair a torn window screen

Replace a shower head or fix a leaking one

Reset a tripped outlet or breaker

Sewer smell in the house

Stop a smoke alarm from chirping

Stop a washing machine from shaking or walking

Thermostat not working or blank

Touch up wall paint so it doesn't show

Unclog a shower drain

Unclog a slow bathtub drain

Unclog a toilet (without the overflow)

Unjam a garbage disposal

Why are my lights flickering?

Ceiling fan not working

Patch a hole in drywall

Recaulk a tub or shower

Sliding door hard to open

Unclog a sink without chemicals
Renter-friendly questions
Should I tell my landlord before fixing something?
For anything beyond basic upkeep, yes. Your lease usually spells out what you're responsible for, and a quick text keeps you from paying for something that was theirs to fix.
What repairs are usually the landlord's job?
Heating, hot water, plumbing leaks, electrical problems and anything that affects safety or keeps the place livable. If you smell gas, see water damage or have no heat, contact them right away.
Will filling nail holes affect my deposit?
Small, well-filled nail holes usually aren't a problem, and patching them before you move out can help. Use paint that matches, or ask whether the landlord would rather do the touch-up.