After the End/Levelling up

Strategies
One of the strategies for levelling up your character in this game is equal upgrade distribution, or in other words, upgrading your 5 stats all at the same time once you successfully level up, you always get 5 points everytime you do and for this strategy, you put 1 on each stat everytime, this is much better for newbies as this will help dampen the difficulty of the game earlier and easier to manage especially while you are still learning, this will also mean that you won't have to worry too much about any sort of points management as every stat is getting improved slightly when you have the chance however your experience increase will be linear so if you are looking forward to reaching the maximum level, then this strategy isn't for you, you will still have to exhaust the monster count for the levels you're playing to get as much experience as possible if you want to level up faster.
 * Equal upgrade distribution

This is by far the only strategy that works pretty well assuming that you want to prioritize a stat when upgrading your character in this game, prioritizing any other stat aside from experience gain is not going to give you a pleasant experience, don't even try doing it as I did the same thing on my very first playthrough, it worked very horribly, so the only real choice is you want to upgrade all stats equally, or prioritize experience gain, now, let's talk about the strategy itself, here what you will do is to put the first 10 points on your Experience gain stat as early as possible, which means your first 2 levels will all go to Experience gain, the bad news is this will make the difficulty spike a lot more difficult for you to take in unless you completely exhaust the monster count for every level you've been (which is what you are supposed to do to make this strategy even more effective and manageable), if you already have experience however then keeping your distance while managing your ammo should do well enough for you, after you max out your experience gain you provide 4 of your points to all 4 remaining stats, and put 1 point for whatever stat you want to improve slightly among the rest, then once you get an another 5, put 4 again on 4 stats, then put your 1 last point on another different stat you want to slightly improve among the rest.
 * Experience gain prioritization

To make sure you don't experience an imbalance you have to keep your upgrades balanced still despite it may look difficult to do so, always put your 1 extra point on a different stat you haven't increased before with your 1 extra point, say for example you put your 4 points on all 4 stat then put your extra 1 extra point on Reload, on your next 5 points, put 4 again on all stats and put your 1 extra point on Ammo, this way, your points are managed well and this will help ease up the difficulty, to help make this strategy even more effective, you must exhaust the monster count for every single level you're in to get as much experience you can as possible, it will take a while but you will not even notice it until you're done, this will make your experience gain exponentially better, and as I said earlier when combined with exhausting the monster count, you will reach Level 10 as early as possible, the stats I recommend to slighty improve first are Reload and Ammo as these stats improve how well you can duel with the mutants especially in close range, with faster reload you can fire even faster between delays which tremendously helps with weapons that do AOE damage such the Rocket Launcher and Sonic Cannon, while Ammo increases your capacity to hold bullets for strong weapons such as those mentioned earlier which not only means you won't have to worry about running out soon, but you can also stock up on more ammo when you get the chance, start by putting 1 extra point in Reload first, then putting the 1 extra point in Ammo, then the rest of your 1 extra point goes to either Health and Ammo first, depending on what you want to improve, then do it again, increasing your Health and Armor really won't do much aside from making you able to take slighly more hits as enemies such as the humanoid axe mutant and the exploding mutant will cut off a huge amount of your Health and Armor if you get hit with these nonetheless, so keeping your distance will make the most difference but that doesn't mean you won't improve them, you will be very soft if you don't improve your Health and Armor.

Level 1 - 80

Level 2 - 120

Level 3 - 150 (with high monster activity)

Draining the monster count on Level 1 could be somewhat daunting, but a good way to know when to leave out of this level is by counting how many kills you've got, if you got at least 80, you are good to go, play Level 2 and exhaust the monster count really hard once more, you can also count if you want, once you gain 120 kills you can leave, somewhere around Level 1 - 2 when this is done correctly you will immediately reach the next level, spend all your points on Experience Gain, play the next level, then drain the monster count hard, gain 150 kills then leave, by the time you've reached Level 4 (Level 4 also has high monster activity), you should have already maxed out your Experience Gain as shown below if you've been draining the first 3 levels really good while also having 5 Experience Gain, starting from here then forward, drain the monster count for each level as much as you can so you can level up quicker and upgrade the rest of your stats as soon as possible.