I have some time so here's some serious advice:
1. Be a spendthrift. Remember that you'll have to pay salaries for your men, and those salaries get higher as they promote. You'll also need to furnish them with plenty of food. In the early game, this means you'll be wanting to spend carefully. Scavenge what you can off of battlefields and be judicious with your coin until you're gaining a comfortable income.
2. Keep your army fed. Linked to the above, make sure you always have access to food. This will be the resource you burn through the quickest, and unpreserved food will spoil, so be careful how much of it you buy at a time. Grains, which spoil slowly, and dried meats and fish are going to be your best friend on the march. (Butter is also an excellent meal of choice.) As your army gets larger, I believe Bannerlord will have new ways of gathering supplies, such as by sending out foraging parties. You can also slaughter cattle, pack animals, and even horses in your train for meat, if I recall correctly. Early on, though, I reckon you'll be buying or looting most of your food, same as Warband.
3. Numbers matter. If you have a bunch of veterans, you can most likely challenge more than your own number if the enemy is mostly brigands or raw recruits. But however well you're doing, be careful that you don't bite off more than you can chew. You might be tempted to say "High morale, riding many victories, my 30 lads can take those 50. Let's go!" But in many cases, even if you do take them, you'll suffer heavy losses as a result. Exercising discretion on when and where to fight is every bit as important as the fight itself. Don't be afraid to run if ambushed by a larger force.
4. Your men convalesce. Make sure you pay attention to how many fighting-fit soldiers you have on hand. You might have an army of 52, but if 25 of them are healing up after a nasty encounter, don't forget that you're at half strength! Rest up in camp or a city until they're good and healed if you want to be safe.
5. Watch yourself. Your health is every bit as important as your numbers; moreso, if you leave permadeath on. Make sure you don't charge recklessly into battle after a tough fight, your health might not be up to the task.
6. Remember that you're human. Never assume you've reached the point where nothing can hurt you. In Mount and Blade, everything can hurt you no matter how strong you become. Maybe you're clad head to toe in steel astride a mighty barded warhorse and you can run down brigands by the score. But if you let your guard down, a score of brigands just might unhorse you and overwhelm you with sheer numbers. Be vigilant, always!