The simple eyepieces that come with telescope sets are a ticking time bomb for astro-frustration. To ensure that this does not happen to you...
Besides eyepieces, there are other telescope accessories such as a Barlow lens, erecting lens and a wide spectrum of filters for astronomical purposes. Here you can find out what's right for which purpose.
In order to be able to comfortably observe with a refractor or Schmidt-Cassegrain telescope, you need a zenith mirror or an Amici prism.
Longer focal length and higher magnification? You can achieve this with a Barlow lens, but when does it make sense and when doesn't it?