I'm not sure how much help I'm going to be, since in the end a lot of these things come down to subjective likes and dislikes, but here's a few thoughts:
* The pattern of "problem, action, result" is often recommended for resume-type writing. The goal is to prove your skills and experience with a concrete example of how you had a problem, what you did to try and fix it, and what the outcome was (usually something positive I suppose, but it could even be what you learnt and how you would go about handling the same situation differently).
If you search for "problem, action, result", there are lots of resources about it on the net. Your first example shows some of this, with the "$500 prize" being the result. In the second example, you describe the action ("designed clearer charts"), but the result is only implied (something positive I assume? x% reduction in inaccurate quotes, or some increase in customer satisfaction, maybe).
* Specifics. 57
This is getting into the subjective realm, but when I'm reading resumes, it really stands out when someone responds with specific things that they've done, as opposed to generic descriptions.
In your first example, what was your business idea? Which university? You say a small team -- could you say "a five-person team" (or however many there were). How did you establish yourself as an "expert on the target market"? You delegated tasks that improved efficiency -- maybe you could use a specific example of why and who you delegated to, and why it worked? In example 3, which youth conference? How many people attended?
I realise the word limits make it difficult to have too much detail, so go for the one or two things that best demonstrate your abilities. You may want to consider reducing some of the sentence lead-ins to give you more words (for example: "Having to maximise the usefulness of the few resources provided"...is it really necessary, or is the lack of resources going to come out in the following detail?)
* Be careful with being vague in describing the activities you performed, as they might not be interpreted how you intend. For example, "I assisted with booking the venue" -- if I was feeling particularly uncharitable, I could interpret "assisted" as "you were in the room while the person with real authority did the booking". Maybe you surveyed and evaluated potential venues? It might be stronger to state this.
Hope this helps. 873