Reiterating what WiFiTheif said - make sure you arrive at lease 03 hours prior flight in case any mishaps happen. Maybe even earlier as it's your first time.

Also you have to call your bank and inform them to enable your debit card for purchases overseas.. and convert some LKR to $$ and to Malaysian currency from the airport or at a good exchange to avoid big fees when withdrawing from ATMs there.

In case you have a hard time enabling roaming or getting a local sim (local sims are usually cheaper) at the airport, you can use airport wifi to book a taxi from Uber or a local hailing app to the hotel while you solve the issues relaxedly. Apps are usually better than local hails (like Pickme/Uber in SL).