'Plans Are Worthless, But Planning is Everything.'

Dwight Eisenhower said this (a few times, apparently).

It's a great philosophy for all kinds of things, especially giving talks. I believe that there are three basic approaches when giving a talk:

1. Plan everything meticulously and aim for perfection. This has the upside that it should be clear that you've put in the work, which your audience will appreciate. However, this approach will also cause you to worry about any aspect going wrong, which is a very unfair level of expectation to place upon yourself. Unexpected things will happen, which could result in you getting severely stressed. Your audience will not appreciate this.
2. Throw some material together last minute and go with the flow. The upside of this style is that you can adapt to things as they happen, giving a natural, conversational feel. The downside is that you may some across as poorly-prepared, you may over-run (your audience will hate this) and the quality of your material may be low.
3. I recommend the third way: put in the work by creating good material and rehearse it several times (re-word it slightly each time to prevent your delivery becoming rote). Then, on the day, go with what you planned, but be ready to deviate from the structure in order to best achieve your goal: engage, inform and persuade your audience. Tech failure? Abandon it and continue giving your talk. Awkward question? Answer it immediately and concisely, and move on. Throughout, keep the plan in mind, but only as a guide. Remember, unexpected things will happen.

So: plan your talk thoroughly, consider all possible eventualities, prepare for each one as best you can, and when it comes to giving the talk itself, relieve yourself of the burden of aiming for perfection. Instead, aim for engagement, brevity and connection.