How can i prevent a blood clot from coming out after tooth extraction?

Leave it alone!: For the first couple days after the ext, don't brush by it, don't rinse too vigourous, soft diet, dont smoke, don't drink through a straw. Give it a chance to settle in and then you should be good, but even if you do all that you are told you can still get a dry socket.

By being careful.: Generally speaking, you want to avoid spitting or rinsing your mouth out for 24 hours. Drinking through a straw should be avoided as well.