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Step 2 and 3 in the depicted manual also help a lot: Step 2: pulling your ear up with the other hand while you put it in. Step 3: After the plug is in, holding it in place (pressing against it) for 10 seconds, so that the foam has time to expand without pushing it out again.
If you do this a few times, they will sit so well that you might actually hear too little (e.g. an alarm going off), in which case they can be loosened a bit again.
Also, I suspect the makers use some kind of water soluble molecule that contribute to its mechanical properties. This ensures that they are disposable because as soon as you wash them with water they lose a lot of their mechanics. I recommend making them last as long as you're feeling comfortable without washing, then using friction from some cloth or tissue paper to wipe its surface instead of soaking it. When you finally wash them, cold water and no soap.
The most effective ones for me have always been the MOLDEX - Pura Fit 7700. They can be bought in bulk too.
Also, your username is quite fitting for this topic.
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I used to think foam earplugs suck because they didn't fit into my ear. Turns out you have to roll them! Sadly the first time I encountered foam earplugs in a library they didn't include instructions. Rolling them they get thin and easily fit into your ear.
Once I knew this they became my favorite earplugs to use during sleep. I used to use reusable ones, but the problem is those inevitably fall out of my ear onto the ground and get dirty. Same happens for the foam ones, but they are cheap (mine cost 0.25 USD/pair), so I just grab a new pair if they are dirty. They lose their elasticity after a few uses, so you cannot use them too often anyway.
The instructions below are from Wikipedia. I don't have a strong preference between different foam earplugs. I usually roll the earplugs between both my hands rather than with two fingers.
By Fornax, CC BY-SA 3.0