There is no way to improve ping from your ISP to the server destination short of changing ISPs. if it's really bad, you may want to switch ISP to one that offers lower latency. Note however that sometimes the lag is route dependent/distance lag and is not your ISP's fault (actually it is their fault since they could get more peers and route it through another path but chances of them doing this for you is basically nonexistent)
The 1st way you can improve it is by lowering the ping from your wireless router to your cable modem if you're on wireless. Ping time to the first hop should be 1-2 ideally. No higher than 5..
Second way is to nag your ISP to fix the ping times to the 2nd and 3rd hops if the ping times are too high. pings to the 2nd and 3rd hop should be around 10, under 20 at least. Basically it shouldn't be too high before leaving your ISP's own networks otherwise you'll get high pings to everywhere.
3rd way is to disable nagle algorithm. Disabling it will likely reduce your latency by half.
4th way is to limit your MTU. Try different values of MTU. Personally I use 368. Beware that it will limit your download/upload speed but you will notice a reduction in latency.
5th way only works for DSL type connections. By switching from interleaved to fastpath, you gain improved latency at the cost of lowered download speeds.
