Before and between servings it's important that you keep your flavoured schnapps and liqueurs in a dark and relatively dry place at constant room temperature, 18-20°C (64-68°F).
Or at least away from heat and direct sunlight as this can cause considerable and unwanted changes in both colour and aroma profile.
Also, to prevent oxidation it's important that you keep your bottles and jars tightly closed.
Unlike wine bottles that are always kept on their sides to keep the corks moist, your corked schnapps and liqueur bottles should always stand right up - or the high proof alcohol in your schnapps or liqueur will spoil the corks.
Over time your schnapps or liqueur might deposit more or less sediments - the small particles that settle at the bottom of your bottle.
That's perfectly normal. It's the same with old bottles of red wine and port wine.
However, when it happens you must - slowly and carefully - transfer your schnapps or liqueur to another clean bottle until the sediments approach the bottle neck.
Then filter the remaining schnapps or liqueur to remove the sediments that will otherwise spoil your schnapps or liqueur.