If you're England, keep a grip on North Sea, that's your primary way onto mainland Europe.
If you're Germany, work with either England or France, choose one to attack the other. In the midgame, set up to take North Sea.
If you're France, become Italy's friend. People tend to underestimate italy but if their hostile towards you, youre in for a bad game.
If Italy, you have choices. Make nice with France, team with austria against Turkey is most common, with you taken him from the sea mostly, and Austria taking from land mostly. You could make nice with Austria and and team with Germany against France, my favorite. Or play nice with France and team with Turkey against Austria. This is rather dangerous, but useful if you can keep Russia and Turkey from working together.
If Austria, you can pretty much do anything besides attack italy. Do that, and Russia and Turkey will come for your ass and you'll have no one to help you. Game over. Your best bet is to get Russia or Turkey to help you take out the other. PLAY NICE WITH GERMANY. ALWAYS.
If turkey, team with russia or Italy agaisnt Austria. You perferably want you and your ally to take most of Austria, keeping whatever non ally from getting much of austria.
If Russia, Team with Turkey and "open south" to austria, or team with France and Germany and "open north" to England.