The basics: Use good quality fountain pen ink or cartridges. Try to avoid own brand inks that do not identify the maker, quality inks for example Sheaffer, Diamine, Waterman or Caran d'Ache are best for your new pen. Never use drawing inks or Indian inks in a fountain pen, look specifically for 'fountain pen ink' on the label. If you do not plan to use your pen for a while rinse it out with cold water and leave it unfilled until you wish to use it once again. Resist using 'old' ink that you have kept for sometime, the spirit in ink causes some evaporation making it too concentrated and more likely to leave harmful deposits on the feed. If you utilise registrar's ink, rinse it out after each day's usage and only refill on the day you wish to reuse the pen. As mentioned modern inks have spirit as part of their formulation, this helps the ink to dry quickly on the paper. However the spirit also dries on the nib feed (the black comb like structure behind the nib) of the pen and will leave deposits that will, in the fullness of time restrict the flow of ink. Regular rinsing will help prevent future flow problems. Keep the cap on when not using the pen for even a few minutes, the cap in place enables the nib to remain moist and ready for immediate use. If you are using a convertor to bottle fill your pen replace it every two or three years, this should prevent unexpected leaks.
Do not screw an ink cartridge in place, better to push it. Screwing can make the opening too large, more leaks. Sheaffer cartridges can be dropped into the barrel end, when the barrel is screwed back it will pierce the cartridge perfectly. Do not take a filled pen on an air journey as the pen could flood with the change in air pressure, This does not apply to the Waterman Edson which incorporates a design to eliminate this. If you are flying take cartridges and load your pen when the plane has climbed to full height. Do not use cartridges that are an incorrect design for your particular pen even if they appear to fit. For example a cartridge may fit but could be slightly too long, when the pen is screwed back together the cartridge may displace the feed, more leaks. Clean barrel and cap with a dry cloth, do not use solvents or strong detergents. Acrylic pens will lose their lustre if you clean incorrectly.
Some customers complain that when using cartridges for the first time in their new fountain pen it is difficult to get the first flow of ink. If you have a bottle of ink, dip the nib first (to wet the feed) then switch to a cartridge. The same tip applies when the pen has been out of use for some time.
Like a quality mechanical wristwatch, fountain pens work best when used regularly. Use your pen, everyday as your first choice writing instrument.
Patina. In my view customers buy fountain pens either because they want to use them or because they are collectors, some do both of course. Pens that are used everyday will eventually lose their newness, they may develop fine scratching or other forms of wear. For many years i did not enjoy using pens as much as I should because I was afraid they would start to show signs of wear. Now I accept the developing patina as a consequence of enjoying a fine pen. I have met customers who have an 'old favourite' barrel all scratched, clip bent, nib looking a bit tired but they are often heard to say that it is one of their most dependable possessions. Enjoy your fountain pen do not keep it in cotton wool in a drawer.