I had attempted to partially soundproof my Alto with mixed results. @Rahat083144 was a great help for me too with basic understanding of the whole process and material selection.
I had zero idea of soundproofing at the time so I'll let you know what I did and also what I now realise I should have done. This was back in 2020 so the materials might not be available any more.
I used two sheets of Buzzmat vibration dampener sourced from Haroon Radio (Karachi) on the front doors' outer and inner skins. The two sheets almost provided complete coverage and I even sealed the inner skin holes with it. It's a constrained layer dampener (CLD) consisting of butyl rubber sheet with aluminium foil layering on top. Although it was difficult to cut but it held strong over ~2.5 yrs. I was stationed at an area with close to 50deg heat during the summer, but there was no melting or smell that people have reported with other sheets. The sheet resulted in no vibration noise from the front doors both outside and inside the car even at high speaker volumes, and the added weight meant that the doors closed with a nice thunk too instead of like a trunk/peti lid like it did before. I would recommend that if you can spare the budget and don't mind the weight go for complete coverage on roof, floor and doors but make sure you use a roller for proper adhesion. It's 3.78kg/sheet(1.11 sqm) and cost me 5.8k back then.
I used 3M sound deadening pads on the inner door skin around the speaker hole since it was easier to cut. It's not a very large sheet so that's all I used it for. 1 each per front door. It's made from bitumen and some elastomers for binding and has no aluminium foil layer. Even if you find this product for sale now, i will not recommend it. I recently sold the car and in order to reinstall the factory speakers, i had to remove this dampener. It had become brittle in ~2.5 yrs and had to be removed by breaking it into small, hard pieces. The adhesion was also not ideal so I am pretty sure this panel was not doing any dampening anymore. Cost was 3.8k total.
I installed closed cell foam (CCF) from AliExpress on the floor. 3m x 1m x 1cm was enough to cover all the way from rear hatch to where the factory "namda" starts in the front footwell. It's soft and highly flexible but will not stretch without tearing, and the thickness seemed more than the quoted 1cm so it was not the easiest job to install the moulded carpet back over it. In hindsight, this is not effective unless being used with layers of CLD and mass loaded vinyl (MLV) which I doubt you'll be able to find in Pakistan. It did provide some sound insulation from the road but I think that was only on account of how thick it was. Cost was $48
If you're just looking to reduce the resonance ("goonj") inside the vehicle, CLD will do the job well. At a minimum, do all doors with speakers installed if you're looking for improving sound quality. Use a thin layer of CCF behind the plastic door panels and you'll eliminate rattle too. Otherwise you can target the floor. Ideal scenario of course will be complete coverage.
If it's complete sound elimination then you'll have to spend big and go for CLD, CCF and then MLV. Most engine noise enters from the front bulkhead and to sound insulate that, you would need to remove the dashboard too. Even then there will still be sound considering how thin the window glass is.
