Deciding where to go is the first thing to do to organise your adventure.
If you are going alone, finding the ideal destination should be relatively easy. If you are going with someone, it's harder, but it should be easy to solve. Agree on your expectations and which mode of transport you will use. A train trip in Europe or touring Europe on a bike are not organised in the same way. You can also choose to mix modes of transport!
However, if you plan to travel in a group, you will have to agree. Discuss what each person expects from a trip: relaxing, exploring, sports... a bit of everything? Once you have determined what to expect, you will be able to find the destination that meets the most criteria. if you plan to walk or travel everyday, check that everyone is in shape to do it without any problem and that the climate or weather is ideal.
You also need to discuss the budget. Going backpacking means travelling on a budget, sleeping in youth hostels, etc. Be mindful that comfort expectations are often different when you are 20 and when you are 40. Similarly, you will not necessarily want to change place everyday. You can rent a flat for a few days to explore a region then head to another place nearby.
If you dream of going to a particular place, prepare your plan for others and describe everything that attracts you to this destination. If you give them an estimate, you should win over your travel buddies! Be careful that they do not mistake you for a travel agency...