Cut it into tiles anyway, but make seamless tiles so you cant see the "squares." I would make a couple seamless tiles of each type you need (sand, grass, water, etc.), You could add things like trees directly on the textures or draw them separately. To make it look especially good you could make transition tiles or put small tiles that overlap the transition with the transition texture on it.
Point is, mess around and see what works. Be creative with it
and look into how to make seamless tiles.
looking at past posts i may have misunderstood the question. Or the question is just way to broad. Probably both. You should narrow down your question to ask about the certain effect you are trying to achieve.