One way would be to make the link between education and employment. Young people are looking for jobs, getting ready to join the labour force. They need to see that they'll get better job opportunities if they have that education from attending French-language schools. These establishments exist, but some programs may not be offered, because there aren't enough eligible people. Students must also have access to support.
It can be scary for an anglophone to study in a francophone environment. It's not easy. However, it's much easier for them if they have support, and if they feel welcomed. The more anglophones join those programs, the more will come. It's more appealing for anglophones if they see it as a possibility.