First of all, be careful in picking a company-

• First off, pick a company that has relatively low beta and is somewhat stable. If the company’s stock is volatile, the thesis can play out quickly, eating into one’s upside or downside. This has happened to me once where my thesis played out right before a presentation rendering a 30% upside to a mere 9% upside. No one is interested in hearing a pitch with a 10% return, as downside if far greater than the upside (in returns, not neccesarily in prices, obviously). 
• NEVER pick a generic company. No one wants to hear another pitch about AAPL.
• Pick a company away from your past experience. This demonstartes that one can pick stocks from a universe where he/she doesn’t have any industry-specific expertise. This criteria is somewhat relaxed in sell-side shops, but not by much.
• Keep the story simple. If it isn’t, make it simple.

The pitch should make it clear-

• How the firm makes money
• Why will they make more money than everyone else?
• Highlight where you expectations differ from everyone else.

Other advice-

• Hand the model alongwith the one-pager pitch
• Understand the economic cycles
• Know what terminal growth rate is implied in the P/E

Advice specific to long-only shops-

• Be excited about the company
• Look for a time frame in the range of 2-3 years over while you expect you thesis to play out