Select one of the Style checking options on the Grid menu to color squares in the grid that are not allowed according to various popular grid pattern standards.
In the American style, every letter must have two words going through it, and no two letters words are allowed. Any squares inconsistent with this will be shown colored so that you know where to correct the grid design. It will also check for disconnected areas of the grid.
In the Cryptic/Quick style, every alternate letter in each word must intersect another word. This standard is usually adhered to by UK broadsheets and elsewhere, though other publications may allow more non-intersecting letters. Two-letter words and disconnected regions are also not allowed.
Select the 2 letter words option if you just want to prohibit two-letter words, without either of the above more stringent requirements.
Use the Custom option if you want to find-tune exactly which rules are applied.
The style checking option can be saved using a template for making puzzles in future.