Depends upon your needs/concerns.
The easiest and most bandwidth friendly option would be to uncheck the box "Use default gateway on remote network" on the client (Connection properties, networking tab, TCP/IP properties, Advanced button, General tab).
End result would be that clients can browse the internet using the same connection that they are using to connect to the VPN. Internet traffic would not pass through your server. Downside to this is that is may be possible for someone to route traffic over the internet, through the client then across the VPN to your network, possibly bypassing your firewall. Should not be an issue, you should deal with it at the firewall level.
If that is an issue, the other option would be to route internet traffic across the VPN, through your server then out to the internet. All of the client's internet traffic has to cross your internet connection twice (once over the VPN and once to/from the internet), so it can eat bandwidth. You would need to configure NAT on the server. Can get kinda tricky, I would guess that you are already doing NAT at your router. Double NAT is not easy and just doesn't work with some hardware combinations and some internet applications.
