you can use difficult and long passwords to increase the security of bitcoin-purses. but remember that on online services you can not recover the password if you forget it . in this case, you will lose all your funds . you can write passwords on the sheet and store, for example, in a safe. you need to provide security on your computer if you are going to store bitcoins in an offline wallet. install an antivirus, but it's better to store data on a flash drive.