1. Drop in bitcoin value: everyone accumulate bitcoin because they want an increase in it value which will yield them profit in a stipulated period of time and in the event that the price goes down bellow the amount you bought your bitcoin, fear might set in but we need to understand and come to term with the volatile nature of bitcoin and still continue holding on to it and that way the momentary loss comes back as a gain after the price of bitcoin has increased.
This point does not relate to security!
It is about risk-benefit analysis before anyone starts an investment.
2. You could loose your private key or an intruder could get access to it.
The point is if you lose your private key or mnemonic seed, you lose your bitcoin.
Who will have access to that private key or mnemonic seed is not necessary related to you because you must assume you lose your bitcoin after losing private key/ mnemonic seed.
So, let's repeat and remember it every day.
"I have to backup my private key/ mnemonic seed safely and my backups must work for me"
3. Beware of hackers and fraudulent people . This is very important at this stage where many persons are looking for newbies and victims that will fall prey to them. Avoid clicking links you are not sure of, their are mails you should avoid responding to and there are some random messages you shouldn't take seriously. Scammers are everywhere and have interesting tactics they can use on unsuspecting individual just to hack into their account. Watch out for them and be as careful as you can.
Don't be curious too much.
Be healthy on the Internet.
Use antivirus/Internet security softwares if possible (not free versions).
Why I put Antivirus / Internet Security softwares at the end, because if you have first two points in control, you even don't need to use those softwares. Secondly they can not completely save you if you fail at first two points practically.