Asklemmy

I assume you are looking for passive methods that aren't air conditioning.

As others have said, thick walls that have a thermal mass. It helps if you open the building at night to help cool the walls.

The structure should be as light as possible, both the walls and roof, to reflect back light.

Windows should have large awnings so direct light doesn't enter during summer. Everything should be in the shade.

If you can, you can create a solar chimney by having a large and dark chimney on the south side of your building. Set your building up so that there is a natural air intake which comes from below ground, so you naturally pull in cool air.

Thick (~1m) mudbrick walls. I lived in a house like that for 2 years, it felt cold inside in summer.

Install solar panels on the roof and use the power to run air conditioning.

Drink a ton of water.

Plant as many plants as possible. Trees are best. Make sure to use species native to your region that deal well with the prevalent weather.

Take an undershirt you're not wearing, get it soaking wet, drape it around your neck

Not sure how your buildings are built over there so this may not apply. But an exhaust fan for the space between the ceiling and roof does wonders to cool a house after a hot day. Those attic spaces get crazy hot and hold the heat well after the sun sets and it keeps your house hotter longer. This won't necessarily help with mid day heat, but help cool the living space as the sun goes down.

Central air conditioning all summer long.

But before I had AC, on hot nights I'd put a cold damp rag on my feet to fall asleep easier and that really worked. I'd also put a box fan in one of my windows pointed outside, and I'd also open a window in another room so that outside air would be sucked in through my home.

I learned to be cool in hot temperature by being still, in the shade, with a breeze, it's very hot and humid here but also windy usually.

Trees help so much. It is noticeably cooler at the park than in the city.

In the house when there is not air conditioning, roofed porches and opening the windows with fans pulling air through the house helps.

I handled the heat by moving from Northern Australia to Tasmania.

There must me much cooler places in India?

Plants and trees

Bucket of cold water, stick your feet into it.

Tin foil in the windows to reflect radiation.

Cold tap over inside of forearms and wrists (iirc ears work well too, but of course a more awkward reach if you're just using a bathroom tap).

drink water, loads of it; if you have to go out, always keep a bottle at hand. wear less clothes and keep your house fresh and ventilated, open all windows if possible. buy a/c for your bedrooms but use them just in the night, when you have to sleep. use fans where you have to work or stay during the day. to cope with the higher electric bill, consider installing solar panels on your roof, or a small wind turbine.

I live in one of the coldest places and most of us don't have air conditioners, but in recent years summers have been uncomfortably warm. I got myself a cheap portable AC and I keep one room cool, it only uses 400W so it barely affects the electric bill. Wet underwear and ice cream help too. I have a small fan with a battery when I need to be in the kitchen.

In our home we have "coolers" (the big kind with metal bodies and large water storage, and padded, perforforated walls). It is outside our house and blowing air inwards. We try our best to seal the area around window with lots of cardboard, fibre sheet and thermocol, and then depending on time of day, confining the space (by closing other doors in home). It is not AC cool, nor is it really effictive when it is hot (50+ C) outside, but other time it works fine. In the nights it does a pretty good job (good enough that i have caught a cold right now). When we do not want the noise, we just run the water pump, so occasional winds from outside come and are cooled by the running water. Water usage is slightly high (we usually require one filling a day, which would be 40-50 litre water i guess), but we sometimes keep cycling between pump on and off to conserve some more water. If noise is a big concern to you, you can try to basically cover whole of the front (with some sound insulating material, like fibre sheets(the polymer ones often found in packaging)) and then make some side channels for air. Or something more simple is using lighter curtains just in front of cooler. This will break the flow of air, but if you have sealed rest of the are, so air can't leak elsewhere, then you would get air breaking its flow and flow around the obstacles and reach you, but not as loud. We do something similar, we have not covered fully, we have left partially open (60 % i guess from the middle) but to cover noise, we partially close it by window (which is kept in place by curtain over it) so we get a tighter channel of air (as it bends around the edge of window). If you stay in the channel, you get large air flow, but more noise, but if you move away from it (from my casse, even by a foot) then the noise is cut in half. The rest of the room is now cooled by this air current mixing with rest of room air. If room is large, t=you may also have to turn your ceiling fan on for this, but we do not have to.

In really peak summers (and peak hours of the day), we use ac for few hours (1-1.5 or 2) and when it gets cooler outside, fall back to cooler.

On top of white paint, if it's legal, try putting up some camo netting above the roof to provide shade on top of the reflectiveness of the white paint. Shades over windows.

Reflectrix on the inside/underside of the roof.

1. It’s a cheap material.
2. It’s quick to install.

Besides that, better insulation and the use of high efficiency heat pumps.

It might be easier near the coast, but opening up windows during times of day where you can catch a breeze might help with the heat the house soaks up. Insect netting on windows may make this a more tolerable option.

Beyond this, the high ceilings in older style homes seemed to make things feel cooler, but I can't really confirm that. A lot of design aspects of older homes were meant to deal with heat, so it might not be trendy but works. I've seen one place with a sizeable indoor pond/pool in the middle of the ground floor, supposedly inspired by courtyard transpiration. The guy was an odd engineer.. no idea about longevity but it did stay cool in that place.

Plants to cut down on sunlight while giving you something nice to look at seems good. Maybe planters for vegetables etc on a flat roof if it's possible.

https://youtu.be/KDRnEm-B3AI

DIY paint. It will cool the surface to below ambient temperature.

My English isn't Englishing atm, bear with me. Heat island effect is caused (amongst other things) due to sealed ground. So replacing asfalt roads, and even brick sealings with green space or even better water, should help regulate temperature. On top of this, instead of white roofs, green roofs are also a good option

Cover the windows from the outside (not inside) to stop sunlight raising the temperature through the glass. I use tinfoil.