Changing Trains in Milan Centrale

Should be easy. Walk to the head of the platform and turn right. If memory serves, the trains to Malpensa go from a platform all the way at the end and set back a little bit. Check the station board to make sure.

That’s plenty of time to even stop for a pastry in the bakery at the airport. The last two times that I made this connection, the train that goes out to Malpensa was one of the far left lines as you face the front of the trains and set back a little. The bakery was at the corner that you walked to between them.

The lines at Malpensa are like tines on a fork, so you don’t need to go on stairways under the train lines to reach the next one.

Another option is the buses to MXP, which depart from via Sammartini, which is the street to the west
of the airport, more or less outside the Mercato. Far left if you are standing outside looking at the station.
The train is a bit faster and a bit more $, I believe, but not much either way.

Any tips to help with a smooth connection?

Get off the Florence train, turn left and walk straight till you see glass doors and the shopping center on the other side. Before the glass doors, turn right and walk straight along the concourse till you bump into a wall. Turn right, walk straight till you find platform 1 to the left of platform 3.

Check the monitor near the track's end to be sure you are getting on the right train. Multiple trains arrive and depart from each track every hour. Platforms 1 and 2 are somehow "reserved" to the airport line, but s**t happens.

Another option is the buses to MXP

Since they are arriving in Milan from Florence by train, taking the bus to the airport would mean a longer walk and lots of escalators. More, even if buses are cheaper I'd never bet a ticket to the US on a bus that could get stuck in Milan's ring road notorious traffic.

I'd Keep the Bus as a "plan B" if I miss the airport train and can't wait 40 minutes for the next one,