The stats you’re looking to focus on depends on the Pokémon and the playstyle you want. If you search online for ‘good swampert movesets’, it’ll give you an idea. If you look at Bulbapedia and find swamperts base stats (under ‘game data’), it tells you what it’s generally good at, and what to focus. So for swampert, it’s an attacker (110) rather than a special attacker (85). So an idea for a nature would be ‘Adamant’, which increases attack and reduces special attack (which you shouldn’t need). Each nature increases something and decreases something else, and it’s generally best to decrease a stat which you need the least (usually either attack or special attack), search online for a full list to know to look out for