Ask the owner's permission first, but most people would be glad to let you look through their scope and discuss their choices in accessories . My first view through my new scope was disappointing. Instead of seeing Mars all I saw was an orange blob. Don't expect to see the dramatic images that are shown in magazines. Photography can capture more light than the human eye.
Large planets are the easiest to see and are bright enough to see colour and subtle detail.
Star clusters and planetary nebulas are the next easiest, with galaxies being the hardest to observe colour and detail. In the end, even a small telescope can reveal remarkable images of planets, nebulas, and galaxies to a trained eye. Two or three quality eyepieces and a 2x Barlow lens should be your first purchase. If you must compromise, buy only one eyepiece and a Barlow and add on later. Plossl type eyepieces seem to be the gold standard.