Finding 4 x 4 puzzles
When you click "New Game", the screen shows the puzzle statistics - success rate percentage & average time. Keep clicking "New Game" until you get a puzzle with a high success rate and low (under 500 seconds) average solve time, before you click "Start Puzzle". The lower the solve time and the higher the success rate, the easier the puzzle should be.
You can also view previous posts for tips and suggestions, print out puzzles and work them on paper for practice; and remember that the more you do, the better you get!