How level does the surface beneath the deck tiles have to be?
interlocking Decking Tiles need to be laid on smooth surface which will not allow them to "rock".
What do I do about corners or curved areas?
Unless you wish to cut the tiles with a wet saw, the easiest solution is to cut a wood or WPC deck tile to fit odd shapes etc. or you could fill any remaining gaps with some suitable landscaping material such as medium sized river pebbles.
Is any kind of underlayment or special surface preparation required?
No, provided the surface is as even as possible with no hollows or bumps.
What skills do I need to install the tiles?
If you played with Lego ® as a child, then you will find laying the tiles just as easy. The tiles lock securely and precisely in place with just a gentle push. Alignment of the tiles is automatic so you just extend the deck in whichever direction you want without any alignment problems.