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Depends on the character class I am looking at and the system. If I'm creating a pure fight character then I boost things like strength and dexterity. I usually make anything around charisma, wisdom or something like that later because for me I can increase those more easily than I can with the fighting attributes.
As mentioned above its all about what you are wanting to play. What class are you playing? Are you going Dexterity based or strength based etc? It's very important to decide this now and get it right. Once you set up your attributes you are pretty much stuck with them. You can increase attributes as you level but it is very slow. Bad initial allocation of attributes can make or break a character. Regardless of class I always try to at least have an average constitution score. You don't absolutely need a bonus to constitution but you don't want a negative costing you hit points every level.