I was going to blog on this after I performed in the first burlesque competition I did but I thought it would be more appropriate to wait as I was due to do at least two, so I could
compare and contrast.
I've now competed in/performed in two burlesque competitions, with another to go. Here are my thoughts:

1) You will get out of it what you expect from it.
Sounds obvious, but from my experience it is very true. If you are going into it as a competition and take the worth of your performance from whether you win or not according to the judging, you will end up elated or disappointed. If you treat it as an experience and a performance opportunity then you will feel satisfied or dissatisfied depending on how you yourself judge your performance based on a variety of factors, regardless of what the judges think. The latter is very hard to do; I told myself I was just in it for the experience but ended up very disappointed all the same, and the fact that I didn't win made me regard my performance in a more negative light than I might have done had it been a straight performance. I'm trying to change this for future competitions!

2) It is very hard to judge burlesque styles against each other, but that's what the judges will do - and by entering, you have accepted this
If you're disappointed you didn't win, place or get the feedback you expected, you can't use the excuse that it's too hard to judge such different styles against each other. Yes, it is, but you knew the acts would all be different styles before you entered, and the judges will be looking for the best performance on the night in their opinion. Note it is ACCORDING TO THEIR OPINION.

3) If you don't win, it's not the end of your burlesque career
No burlesque competition can claim to be the be-all and end-all of burlesque competitions, nor the ultimate standard of burlesque excellence. In fact, most burlesque competitions have deliberately named themselves so that the winners cannot claim to be "britain's best burlesquer" or similar, but they can say (and proudly) that they are the winner of the "Tournament of Tease" (for example). It is the opinion of the judges on the night, who will be influenced by as random a number of factors as those by which your performance may be influenced. They may have already seen several excellent performances and yours may be just one of many, whereas on a different night against a different set of performances you may have stood out. Similarly, you may have been feeling under the weather, or have had a costume malfunction that put you off your game. It's all part of the randomness of competition.

4) Most burlesque competitions in Britain encourage newcomers to provide them with the opportunity to perform
But they are not limited to complete newbies! These sorts of competitions will attract more experienced performers as well as complete newbies. Don't be put off if you find yourself performing with others who are far more experienced, it will be of no use to you to compare your performance to theirs as unless you are very talented (and I have seen amazing first-time performances) you will probably find yourself, in comparison, lacking in some respect. This is to be expected! Those experienced performers have worked hard to gain their skills and polish and I would expect to feel below their level. What you can do is learn from them.

5) Ultimately, as a newbie, I would treat competitions as learning experiences.
Listen to what the judges say if you do get feedback and take the comments that you think you can use on board. If they say something you strongly disagree with, it's not gospel - only you can decide whether you should change your act based on what they say. Any performance will get you exposure, another performance and venue to list on your CV and another go at performing that act. All of those things to me make competitions worth while, but if you feel that any negative feedback will stop you performing, maybe you should consider avoiding them.

Exposing yourself (literally and metaphorically!) in any public arena will always invite positive and negative responses. If you feel you won't be able to handle every kind of response, maybe performing altogether isn't for you.

For me, I look forward to my next competition and what it may bring.