timing for pregnancy

Hey everyone! So we're trying for a second baby now and we already have our boy and would like to better our chances to have a girl, either way I just want a healthy baby, but some people have said the earlier you have sex before ovulation the better. Has anyone ever tried this? And Should you have sex before ovulation all together or just a few days away from your peak? Like 3 days before. Any help is  appreciated! Thanks :)