Hi BeatleJohn,
Skywatcher plossls that come with these scopes are
reasonable quality.
More expensive eyepieces can give you better contrast, a bigger field of view, or the ability to zoom. But these can cost a lot as mentioned.
The best advice to anyone starting out is to get yourself along to an observing session. Some are mentioned in the Star Parties Forum. Many of these are free to attend and participate in. And regulars are keen to share their knowledge and advice. You may also be able to try some premium eyepieces in your scope to see what works for you. Where are you located? Your profile does not give anything away.
Generally, planetary objects worthy of your attention for seeing detail are limited to the moon (best when less than 50% illuminated), and of course Saturn and Jupiter.
Mars is showing a bit of detail at the moment, but it can be difficult even with much more expensive equipment, and often does not provide much joy. Venus shows no detail due to its cloud content. Other planets, will give you a warm fuzzy feeling inside just for finding them, but will have no more detail than a very small dot in your scope.
Increasing magnification does not always increase viewing pleasure either.
You really need good atmospheric conditions to pump up the magnification much above 150x with most setups. And your 10mm plossl will be delivering 120x magnification (if I got your scopes specs right 1200 fl).
Above that, it may be difficult to get a sharp image, although technically, your scope is capable of 306x magnification, atmospherics will rarely allow this to be a pleasant experience. [And a standard 4mm plossl will be like trying to look through a straw]
Anyway, after you get you fill of planets, you will want to move on to Deep Sky Objects (DSO's) and then you will be heading the other way, to get smaller magnifications and bigger Field of Views. This is where the premium eyepieces come into their own, with better contrast, and larger field of view.
A lot to take in I know. We all start off pretty much the same, and I for one am thankful of all the help I got at our local observing sessions, and equipment I got to sample there. [We meet at Mangrove Mountain just north of Sydney]
Anyway, keep at it, ask questions, and enjoy the wonders of our beautiful southern skies (assuming you are southern hemisphere located ? )