here what I do at shell

old style where you can see RM10/20/30/40/50 preset button

1) insert credit card and the machine will tell you to wait for processing
2) once done, machine will tell you to remove your card, so take it out
3) go to pump machine, press the preset button RM10/20/30/40/50 for your desirable amount of money of petrol or
3) press the button on the right, RM or Litre, then manually press the number pad 1-9 to key in the amount of money or litre of petrol to buy
4) lift up the nozzle and shot
5) once done return nozzle and buang the receipt

new style where you see buttons P/1/2//4/5/-/10 button

1) insert credit card and the machine will tell you to wait for processing
2) once done, machine will tell you to remove your card, so take it out
3) press the button on the right, the one with a money sign (a notes looks like a USD, 3rd or 4th from the top I cant remember exact) and you will see the '0' moving on the screen between RM and Litre, stop where you like, say I stop at the RM, then tekan P1 for RM10, P2 for RM 20, P3 for RM 30 and so on (Sorry, I never try on Litre, not sure)
4) lift up the nozzle and shot
5) once done return nozzle and buang the receipt

You still can pump until full lah 

I never use preset, so I cant answer your question. I just pump full 

For shell, bonuslink > credit card > pump until full

Weekdays, I use OCBC mastercard.

Amex gives 5x treatpoints everyday, no cashback on weekdays
Visa/Mastercard only gives 1x treatpoints.

So, always go with Amex.