I tried removing push redirect gateway def1 from server config file, after which client is not able to connect to internet
I think you want to figure out why this happens first.
Other than this, it's really about firewalling in the server. Something like this should do:
iptables -A FORWARD -i tun -o eth -d host_or_network -m conntrack --ctstate NEW -j ACCEPT
iptables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i tun -j DROP