If chronic lateness has taken over your life and turned into a defining trait of who you are, it's likely that you're losing out on job offers, recreational opportunities, friendships, and more. If you are showing up late to your own life, get organized, prioritize punctuality, and address any underlying causes.
When you have to be somewhere, try to arrive 15 to 30 minutes before you need to. If you always run late, that means you must be failing to account for something you always do. Anticipate that by giving yourself extra time to arrive. Keep track of whether or not you actually do arrive early. You might find that leaving early gets you to places exactly on time.
Set two alarms. Set one alarm that lets you know it's time to drop what you're doing and a second alarm that means you need to walk out the door. Obey the alarms. As soon as the first alarm goes off, stop what you're doing. If it's something you'll be coming back to, like a project for work, make a note to remind yourself where you left off. Grab everything you need and make sure you know how to get where you're going. Aim to be out the door and on your way before the second alarm rings. This will only work if you take the alarms seriously, so make sure you react as soon as you hear them.
Prepare for the day ahead. Have all of your notes and materials organized well in advance of each event, so that all you have to do is grab them and go when it's the actual day. If mornings are a struggle for you, do as much as you can to ready yourself the night before. Before you go to bed, lay out your clothes and pack your bag for the next day.
Learn to leave time in between tasks and meetings. It soon becomes unbearable to shift between one meeting and another without space in between. If you overschedule yourself, however, you'll arrive late as soon as you hit a bump. As well as giving you space, this time also acts as a buffer between events, which can be borrowed from, should you be held up in a prior meeting, allowing you to still get to the next one on time. Calculate transit time between activities and then add 10 to 30 minutes for unexpected delays.