Her Majesty's Court Service has a Small Claims guide here
You can download all the forms you may need as well as guidance leaflets
If your claim is over £5000, you may be allocated to Fast Track. See the guide here
There is a good guide to the County Court procedure at the Just Claim website here
Although not specifically for bank charge claims, it has a clear concise guide to all the various stages, including a step by step guide to filling in N1.