In most supermarkets you can find good Dutch and Spanish ice berg lettuce. Make sure its green and not brown. Mushrooms shoud be as white as can be unless you use tasty brown coloured mushrooms (i cant think of the proper name right now) but the have the same shape as a regular mushroom.

Its important to dry the lettuce completely after you wash it!

Wash the mushrooms BEFORE you cut them and do not soak them in wather this will eliminate the taste/

Roast some nuts in a skillet to add to the salad/

Use some walnut oil or plain oil and vinegar.

Use the small cherry tomatoes

Hope this is usefull.

Jeroen