Guild Wars is a fairly forgiving game. It's hard to paint yourself into a corner. Leveling isn't much of a grind, you can change your subclass, and even when things go bad, it isn't difficult to get a do-over. However, especially if you're new to the game, you'd probably prefer to avoid as many "newbie" mistakes as you can.
If you care about unlocking all the skills in the game, chose your class combinations carefully. Don't waste time leveling up a Monk/Mesmer and then a Warrior/Monk, unless you really want to, or you're not keeping tabs on skill gathering.
To help you out, we've compiled a list of 20 Tips n' Tricks at Guild Wars - TenTonHammer.
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