Short answer
Only an amount you'd be fine losing completely. Many traders cap any single memecoin at a small slice of a trading budget that is itself money they can lose.
Start from the assumption that any memecoin can go to zero, quickly. Then ask how much you could lose on one trade without it changing your mood, your week or your bills. That's your ceiling, and many people go well below it.
Spreading a budget across several small positions means no single rug ends your session. It won't stop you losing money, but it does stop one bad call from becoming a disaster.
If you copy traders, apply the same thinking with per-trade caps and a daily budget, so a trader's bad day can't become yours. See how copy limits work.
See the checks for yourself
18+ only. Self-custodial: you keep your keys. 0.5% per trade, no minimum. Memecoins can go to zero.