How many times you got cought with heap of staff not fitting in your hand luggage / baggage allowance while packing. To be fair, most of the people are not using at least good quarter of their clothes and other items packed in their bags.
I’m using importance / priority approach. Most important things first, the rest going in only if there is a space for it. All other things I may have a doubt about are usually left on a side to come back to reconsider it later.
One of the most important rules: Do not overload. Extra weight will always get in the way while you travel and can kill all joy from your travels turning you into sweaty mule. Shed as much weight from your gear as possible if you not kin on torturing yourself and creating unneeded challenges.
Lets say if you can get away without computer – take your iPad or tablet instead. If you may not need an iPad, take neither.
Clothes, only take ones you 100% see yourself wearing it and will have a time to wear it. For example what is the point in taking 10 T shirts if you going away for 7 days only. It applies to all other clothes.
Other gadgets & toys: try to minimise space and weight on every each of them. Let say you have a choice between light and slightly heavier item that function in about same way choose a lighter one. Use universal chargers and cables instead of taking charger and cable for every item. Stick all heavy items in your baggage and ligher ones in your hand luggage. Always account for unforeseen situations and have all essentials in your hand luggage, shall you baggage gets delayed or lost in transition or during transfers. Make sure you keep your travel money in 2-3 different locations. Lets say some with your passports, some on you in easy to rich location as spending money, some in your bag and etc. Remember: keeping all your cash in same location is very bad habit. Never leave any important documents or money in outer pockets of your bags. Always use code locks on your bags, there are lots of fancy looking ones so you can even turn it into fashion accessory!
and most important, have fun !!!