What can speed up play in golf?

Key factors are to move fast between the shots and always be ready for your shot when it is your turn. This includes reading your putts while others are putting.

More about playing fast in golf

An average round of golf for a group of 4 players should not take longer than 4 hours.

Here are some tips for quick play in golf

Always keep up with the group in front. Alert your group when you are falling behind.
Be ready to play your shot and be prepared to hit out of sequence if a player is not ready or able to hit.
Read your putts while others are putting.
Have tees and a spare ball in your pocket.
Shorter hitters should hit as soon as the group ahead is out of their way.
If your group is falling behind, players who have finished the hole should walk to the next tee and tee off while others still are putting out.
Record your scores on the card on the way or at the next tee, not at the green. Score while others are hitting, not when it's clear for you to play.
Unless the siren has sounded and play has been suspended, keep playing no matter the conditions. Others behind you are still moving. Play, or if the conditions are beyond you, leave the course.