In every position given below these ideas can help you find the solution

1. Identify the ambush. Which piece is hiding, which piece is covering it? Since it is a double check location of opponent's king should be a major clue. 
2. Once you identify the ambush identify all the possibilities of uncovering a check, some possibilities would be better than others.

Black just sacrificed a Queen with 1)...Qg2+!! White have no choice but to take it. 2)Kxg2 and now Black uses double check to give mate in 2 more moves.

Similarly to a previous problem Black Queen attracts (using its charms, an offer that cannot be refused) opponent's King to a square where it gets mated.  Black mates in 2 moves.

White gives a double check. 2) Forces black rook onto a square that completes locks the Black King and delivers a mate with the remaining Knight.  This construction is know as the smothered mate. Mate in 3 moves.

White mates in 3 moves. Hint: did you read through the lesson?

White just sacrificed a Queen with the last move 1) Qd7+!! and after the Queen was taken 1)...Bxd7 White finds a 1)double check 2)Check 3)Distract the defender from defending the last rank. 4)Mate. White Mates in 4 after Bxd7. (Long, harder, problem)

Queen trade1) Qxg8 Rxg8 is bad (R vs B) left. There is a tricky way to distract opponent's b8 Rook from the defense of the Queen.  If King captures instead a  double check blocks Qg8 protection. How?

White gives up a Rook to attract opponent's King to a square where it get mated. White mates in 2. Another Rook will take the banner from a fallen comrade.

White sacrifices a Queen and if Black takes they get mated by a double check. How?

White wins a Queen using double check