At the end of each presentation, you are most likely to find yourself thinking about it, even if you don't intend to. It is always useful to reflect back on your performance during each presentation, to try to identify aspects that went well and, of course, what went wrong.
Your presentation could be a success or a failure in the eyes of your audience, but in your eyes, the results may be different. In order to find out whether you have done well or not, you need to assess the results. There are several ways of doing this:
1) Observe the feedback from your audience afterwards. This tells you a lot about whether they enjoyed your talk or not.
2) Look at the quantity and the quality of enquiries you receive after the presentation. If people ask meaningful questions, the chances are they enjoyed your presentation and understood your ideas.
3) If it is a sales presentation, the obvious positive result will be securing a sale. However, on many occasions, you may deliver a good presentation but not a winning one. This may be because your product is not what the customer is looking for. This is not necessary a failure on your part.
4) If you have friends in the audience, ask them for their honest opinion afterwards. they are the ones who can tell you how you performed from the audience's point of view.
5) If you have the facility to record your presentation on video tape, do so and watch it later. This gives you the most honest opinion of all. A camera does not lie, it tells you the truth, the whole truth and nothing but the truth.