First of all, don't be scared. I was a bit intimidated that I would be shown up as a rank amateur straight away and the hairy, burly men behind the counter would laugh and throw me out of the shop. It is true that they do most of their business with builders and professional craftsmen, but they are well used to the DIY enthusiast as well. Ask them what you need for the job.
Tool hire shops have a very simple business model; they own tools, they rent them to you at a daily rate. They take a sizeable deposit for security (on one occasion I returned the tool so quickly, they actually owed me money). As a rule of thumb I would bring sufficient money to pay most of the cost of renting. You settle up the outstanding amount when you return the tools.
At the point of renting they normally take down some details about you such as name, address and phone number. They may require some form of ID to back these up, a driving license is perfect. They will give you a receipt with the deposit recorded on it, so keep this and bring it back when returning to prove what you've already paid.
I would recommend trying to book a tool if it is reasonably crucial to the job. Overruns on hired tools are very common and it can really ruin your DIY plans if the previous hirer decides to keep something over the weekend. This pays back on the other hand in that if you decide to keep a tool longer, there is no problem. I would ring and tell them though out of courtesy. In short, there is no guarantee that they will have it when you need it.
I don't know how it works around you, but in Limerick it is very efficient to rent close to the end of the business day on Friday. You will then have the tools for the entire weekend and only pay the rental for Saturday.
For our floor sanding job for example, we found that we needed 3 sanding tools; a floor sander rented for about 25 quid a day, a belt sander for about 20 quid and a heavy duty orbital sander for about 10 quid. I would rent them at 5pm on Friday and return them at 8:30am on Monday.
Ask them to show you how to do the regular stuff like changing belts / sheets / blades etc. You can loose loads of time later figuring this out for yourself. You more than likely won't get instructions with the tool.
A lot of the tools may be 110 Volt, if this is the case make sure that they give you a transformer. There is usually no charge for this but they do seem to trip the house circuit breakers a lot. Try and make sure that the lead between the tool and the transformer is as long as possible. If it is too short, you will be forced to lug the transformer around with the tool and they are bloody heavy.
Try not to use the words "black" and "decker". This seems to be an insider's joke with them and they will lecture you about "professional" versus "hobby" tools. There is usually a prejudice like this in every walk of life.
Well that's it. Hope our experiences were some help. Add an entry to the guestbook if you have any comments.