Bridge Chestnut 2 - "Always lead the top of partner's suit"
This is NOT a good idea. It can easily cost a trick. e.g.
Here, if you lead the King, declarer will win the 3rd trick in the suit with his Queen. If you lead the 3 instead, partner will win his Ace and return the Jack. This scoops up declarerís Queen so that he makes no trick in our suit.
Instead, our policy should be: When leading partnerís suit, make the same lead that you would always make from that holding in the suit.
Your natural lead from K53 is the 3. So, that is the card which you should lead.
This may mean that, against a suit contract holding Axx in partnerís suit, you may not lead the suit at all. Partner can work it out! Of course, there are exceptions....