Here are some important requirements for your existing flooring before any installation of carpet, carpet tiles, rubber flooring and vinyl tiles.
The floor has to be flat, no holes, cracks, dents. Cleanliness is important as well. Please keep the floor clean and rid of rubbish and dusts. Any uneven parts of the floor should be evened out. You can do so by doing self leveling using cement.
Calculate the width and length of the room to be installed. The material must be cut to around 20mm more than these measurements before installation. Crop out the excess material only after sticking/installing the carpet or rubber flooring rolls.
To make the 2 joined carpet rolls look natural like one complete roll, ironing the two pieces of carpet rolls together is required in the installation process. Alternatively, you can also double sided tape. If the installer is experienced, no ironing or tape is actually required.
During installation of carpets, there may have small ceases. Do not worry as eventually it will be smoothed out using professional tools by the installers.