That is the million dollar question my friend. The first trick is always to put in only what you can afford to lose, just bang in what you’re comfortable with.
The next step I’m taking is looking at the risk v reward. Personally from 5k I would consider the chances of the price levelling at 2.5k to less than it levelling at 10k in the next few years. Likewise I think it levelling at 2k is less than it levelling at 8k (I don’t mean touching these prices I mean levelling out there).
I would never encourage people to do what I do though. Each to their own. Perhaps use it as a swear jar instead of a “Proper” investment and stick a couple of £$€ in occasionally?