How to rent good equipment easily and cheaply
The key to getting the most from any hire house is transparency and honesty. Most rental houses do want to help out where they can, some are more willing than others but all of them just want you to be honest about what it is that you need.
Firstly, you must respect that they are a business. If you're expecting something for FREE, do not go in with the attitude that you have the right to what's on their shelves - you don't! Where you have a budget for equipment, be honest about what your budget is - even if it's small, it helps many companies justify the risk of letting the kit out the door. It is often student and low-budget productions which do most damage to kit, so be careful about playing the student card. If your DoP/sound guy etc.. are industry professionals - let them know!
Secondly, be flexible about what it is that you want. The best thing to do is to tell the rental house your *ideal* kit list. If you are very lucky, this kit might be available to you and may be within your budget. However, if you're paying little to nothing for the kit, the rental house will often say that if someone comes in willing to pay for the kit, or pay the going rate, they'll get priority. In this case, make sure that there is a backup kit and work out what that backup kit would be.
Thirdly, don't be afraid to ask big companies. Sometimes the largest rental houses can be the most useful because they will have excess inventory. The winter months in particular may be quite quiet for them so "losing" things off the shelves for a week or two might not go as noticed as it would in September.
That's it really - just be honest, transparent and realistic and more often than not you will find someone who can help you out. Just remember them when you get that million dollar feature!