The biggest change when you hit the open road on your motorcycle isn't actually physical, it's mental. Most of us who commute daily are used to concentrating for short bursts of time. An hour or two of traffic poses no issues. But if you're planning a six hour riding day, you're committing to that same level of concentration for thrice as long. If you're not ready for that, plan for shorter riding days. Concentration, and your ability to maintain it, should also determine your pace. No superbike rider hits the highway and cruises at 160kmph. Not just because it's illegal, but because the effort of focusing that hard to hold that speed would wear you out. Pick a speed where you are most comfortable; this is where you'll go the longest with least effort.
When out on long rides, the next thing that comes up is luggage. You can use anything from an old rucksack to purpose-built saddle bags. Ensure that the bag is securely mounted - it shouldn't move around over bumps, it shouldn't slide down the seat into you and it most certainly shouldn't have dangly bits that might snag in the wheels or burn off on the exhaust. Motorcycles are the ultimate teachers of space management. Roll up clothes into tight rolls to save space, carry only as much as you will need and the tighter you pack your bag, the more secure it will be mountable. If you pack the heaviest things at the bottom, you'll feel the least effect in the handling of the motorcycle. If you tour often, it's worthwhile to invest in purpose-built motorcycle luggage - like the relatively inexpensive saddlebags/tankbags from Cramster (cramster.in).
Remember that in-saddle stamina and touring are two entirely different pursuits. Stop often - it'll give your muscles a rest, and allow you to concentrate longer and feel fresher. Hydration systems like the ones from Camelbak help endurance hugely too.
Finally, if you are planning a multi-day trip, keep in mind that you will be freshest when you leave. Plan to cover the greatest distances early in the trip, and the riding days should get shorter as you get deeper into the trip. This is not only safe, but allows you to see more in practice, since you spend the meatiest of the riding days at a more leisurely pace, stopping to see things you would otherwise just blow by.
Tip: Highway traffic respects motorcycles far, far less than in town. Wear reflective, brightly coloured gear so you are visible and avoid as far as possible travelling in the night. Keep your cellphone charged and let someone know your plan before you leave. Add a medical info card to your wallet (add blood group, known allergies and emergency contact information) just in case. Above all, remember that you're doing it for fun. If you're tired and feeling worn out, stop at a hotel and take a long break. Far better to arrive late than to arrive tired, frustrated and angry.