If you want to invest in altcoins for the long-term you should consider some fundamental tokens that have real use-cases and good projects under them. First of all, consider tokens of different alternative chains such as Fantom, Polygon, Polkadot, BSC, Near etc. If you are tolerant to risks, pay attention to tokens from gaming sphere and metaverse as they are very trendy now.
If you see that the coin have an unstable market movement then you should try to make quick cash out as there may be possible pump and dump event in the coun market.