While I'm reluctant to give away "tricks of the trade", I'm not as reluctant to help out newer players. :)
One classic trick is the "fast retreat home". Basically, if your home centers are threatened but your armies are far away, if one of your (far-away) armies gets dislodged, just disband it instead of retreating it, then you can rebuild it in a home center, where you need it.
Example: You are Russia, fighting it out with England, but then Turkey suddenly decides to attack you, and you have enough forces to defend against the English, but not the Turk. The English dislodge one of your fleets in the Norwegian Sea. Instead of retreating it, just disband it, then next build phase, rebuild it in Sevastopol, where you need it more.