The first thing to do is congratulate yourself for finding and reading this article.
The worst thing you can do when your work is going to be late is bury your head in the sand and allow the situation to get worse, simply because you didn't deal with it.
The best thing you can do now is work out the most effective way to minimise the stress, difficulty and impact that you work being late will have.
As soon as you realise that you are behind with a project, ask advice and enlist help. If at all practical, speak to your line manager and explain the situation. This explanation may take some planning - don't just blurt out the first excuse that comes to you. Think about why your work is late. Did you just leave it too long to start? Did you get too bogged down with the planning stages so now the project needs completion you have not allowed enough time? Have any details of the project changed since it was assigned to you?
Do Not Make Excuses
You must not just come up with a list of excuses, or your potential lateness will simply be seen as an illustration of your incompetence. You need to be able to explain why the project is running late, what you can do about it and what resources you require. If, for example, the project is a report that is due to be written up and you have only just finished the research, request an extension. If you do this in plenty of time, you will be able to show you are conscientious rather than lazy. If, alternatively, there is any way for you to pull out all the stops and have the work finished, you may need to be prepared to put in a few long days.
If you are already doing everything you can to finish your work but have that sinking feeling that you cannot complete it in time, you will need to come clean. The most honest you are, the least badly this will reflect on you. If you are unable to request an extension, you may be able to complete a draft of the work, or write an overview of the project. This, as long as you have explained it to those necessary, before the project meeting, should suffice and enable the meeting to go ahead. Just make sure you complete the work as soon as possible and keep your colleagues informed.
Don't Be Too Apologetic
It would be unwise to be too apologetic about your tardiness. You will need to explain why the project is late, have the overview available and ensure you finish it quickly, of course, but if you keep apologising or being too humble about it, it will seem like a bigger mistake. You will be surprised by how easily it will be forgotten if you do not keep mentioning it. As long as you offer practical solutions to any issues it may affect and complete all other tasks effectively, you will only be judged on how well you have handled the problem, as opposed to the problem itself.