1) Keep your finances in such disorder that you have no idea what the balance is in any of your accounts. This means that at the cash point you will want to check the balance for every card you have. If you are shocked, which you probably will be as the balance will be less than you expected, then you can take even longer as you question how and why.
2) Have no idea how much cash you are going to withdraw. This is simple. If you allow your cognitive processes to stop at "I need some cash", then when it is your turn you can pause and ponder as you try to decide how much to take out. Note, this works particularly well when coupled with the previous point. To achieve maximum effect, do not even think about how much you want to withdraw when you are in the queue.
3) Do not get your cards out ready before it is your turn. If you do this particularly well, you will have to rummage around for minutes to find your wallet or purse.
4) When it is your turn remember that there is no rush. You had to wait, and the people queuing up behind you can wait too. Aim for inefficiency. Check your balance, be shocked, check another account's balance, be shocked again, then have a think about how much you want to take out. Again, don't rush. Now is the time to think about what you are going to be doing that day and how much cash you need. Add it all up in your head. Advice slip? Have a think, don't be forced into any quick decisions. Receipt? Have another think, do you or do you not want a receipt? Take as much time as you like.
5) Accidentally press Cancel so that your card is injected. Then you will have to wait a few seconds before you can insert your card, re-enter your PIN etc. Do this several times.