If you have an investment portfolio, I think 5-10% is a smart initial investment, putting all of it in as soon as possible. Do not buy any more, or sell any more until it is overvalued - it is extremely undervalued right now so do not delay. Once it gets overvalued, start selling it off one or two percent at a time as it continues to reach all time highs. Once you have half of it sold off, this should be at a price point that is way above what most people think the bubble would go, if it ever gets that high. Keep this in liquid assets until bitcoin gets undervalued again like it is now.
At that point, but more coin, but also spend some of the profits to help with whatever you wish to accomplish with your life.
I got in at a $25 cost basis with 5% of my portfolio, but I really had trouble deciding to buy or sell, so I did both - and lost at least a third of what I should have had I held, through 2 bubbles. It is very stressful to get rapidly wealthy in unrealized gains. Keep a cool head.
If you are in the US as I am, then you should realize your national currency is in very great danger. I keep hearing 60 trillion of debt now - I fear all our dollar-denominated assets are at risk of seizure by the demonic international bankers who control our politicians. Soon that 5% initial investment will become 80% and higher of your net worth. At that point your bitcoin profits should remain at least 50% invested in bitcoin. The wealthy are buying collectible items like rare art masterpieces. Maybe that is a good place to diversify. A little gold might be good to have. Silver seems really heavy/bulky in larger amounts.
I did not understand how to determine bitcoin is over or under-valued until after the last bubble crashed, unfortunately, so I am waiting for the next bubble to exercise my new-found wisdom. Not everyone agrees with this model of valuating bitcoin for trading purposes, but it is important to decide your sell and buy strategy in advance before the rapid price increases (and drops) create alot of stress.
here are some good links I would recommend:
https://bitcointalksearch.org/topic/stephen-reeds-million-dollar-logistic-model-366214https://bitcointalksearch.org/topic/m.7072418