Look at the top X cards of the deck in secret. From these cards, resolve the other effects (Draw, Tuck, Trash, etc.) of the Consider effect in their listed order. Then, if there are any cards remaining, place them back on the top of the deck in an order of your choice.
For example, to resolve “Consider 2: Draw 1, Trash 1”, look at the top 2 cards of the deck, put 1 into your hand, Trash 1 of them, and then put the remaining card back on top of the deck.
If you are resolving a Consider effect and there are insufficient cards remaining in the deck, look at as many as you can and resolve the other effects in the order listed as much as possible.
For example, to resolve the previously explained “Consider 4” effect, if there were only 3 cards remaining in the deck, you would Draw 2 and Trash 1.