Always On Top!
When going through flashcards shuffle the same card to the top over and over again. This is great for holding attention, building focus and language repetition.
Repetition is an important part of acquiring language. But if it is dull it is more of a hindrance than a help. One simple technique that makes repetition entertaining and which is easy to master is shuffling a flashcard to the top.
Generally when introducing new vocabulary I work with 4-8 cards, depending upon the age and experience of the learners. I shuffle the cards and wait for someone to call out, "stop!" (Children are quicker at this than adults...). I show the card and name it it and then start shuffling again.
There are several ways to shuffle the same card to the top. With a large group of noisy children it is very simple. Just stop when the card is naturally on top. Another way is to shuffle the cards by taking cards from the middle of the deck and moving them to the back. The top card never moves. Alternatively, press with the thumb to create a vice. Then take the top card and a couple more and split the deck. The cards go to the back but then bring the top card to the top again leaving the others behind. This assumes you are holding the cards so that you can see the top picture and this is the one you want to show to the students. Experiment and find a way that works for you. Even if the students realise you are shuffling to the top it doesn't really matter - you are not setting out to perform a magic trick even it looks like one.
Once you can shuffle a card to the top you need to decide how to stop! One way is just to allow another card on top and repeat the process. Another way is to make a show of being exasperated with the card and physically remove it from the deck. With very large groups this can be made into a performance. Take the card and tuck it under your arm. As the cards are removed find silly places to put them. I've ended up with a card under each arm, between my legs, under my chin and even in my mouth. If reviewing cards (rather than introducing them) placing a card in the mouth is a good way to encourage children to call out answers. They quickly realise that you can't say anything!