I don't know now that you'd like firewall setings for servers or desktops but I think that for desktops it's enough this simple rules:

iptables -F



# Security policy



iptables -P INPUT DROP

iptables -P FORWARD DROP

iptables -P OUTPUT DROP



# Accept loopback



iptables -A INPUT -i lo -j ACCEPT

iptables -A FORWARD -o lo -j ACCEPT



# Incoming and forward rules



iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT



# Outgoing rules



iptables -A OUTPUT -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

If someone want, can also log traffics and attacks attempt :)