The most important care factor is remembering to clean your fountain pens nib from time to time to avoid it clogging up with dried ink. It is usual for a fountain pen to build up dried ink over time and depending on the types of ink you use your pen will require more or less cleaning. Lamy fountain pen ink for example is known to be a slightly wet writer and therefore won't clog as quickly as other ink brands. Also any black inks tend to dry in the nib quicker than other colours due to the types of liquids needed to produce a black ink. The best way to clean your fountain pen nib is to simply run it under cold/warm water if you are in a rush or can't remove it from the pen, or if you can remove it leave it overnight in a cup of water (nib section only). It is recommended you flush your pen once a month or if you won't be using it for a prolonged period of time (I hope not!)
Should the nib on yor pen become twisted, cracked or worn down we recommend you contact a professional nib repair service. This is especially important for vintage and expensive pens where trying to DIY can be costly and do more damage than there was in the first place. There are many different fountain pen repair companies around the world and some even specialise in specific brands such as www.penhome.co.uk which are a certified repair shop for Waterman Pens and Parker Fountain Pens.
This applies for the fountain pen body as well, simple research on the web will show you that there are expert repairmen for fountain pen body care and it is up to you to decide whether the cost involved is worth it to save your fine writing pen!