A good shape should do some of the following:
Maintain a connection (because it is always easier to have to take care of one group instead of two)
Be efficient (you want the best possible effect with the least possible ammount of moves)
Create Eye potential (so you can live easily)
Maximize Liberties (so you can win capture races)
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If you wanna practice ladders just set up the starting shape on a board. And then take handfull of stones and throw them softly in the direction of the ladder. Then try and read out whether the ladder works or not before playing it out.