When sending lumens to an account for the first time, just send 2 lumens at first to make sure you have the correct account ID. Once you confirm the transaction went through correctly, send the remainder of the desired transaction value.
Use the memo field for exchanges
Because many exchanges store all users' lumens on one account and identify your balance based on unique memo, you must include the memo exchanges give you in transactions into the exchange. If you don't include the correct memo, your lumens may disappear into a sea of other users' lumens.
Never give out your secret key
When transacting on the Stellar network (or any distributed ledger), never input your secret key unless you are using the Stellar Account Viewer or Laboratory.
Avoid "web wallets"
As we saw with the Blackwallet hack, a "web wallet / account viewer" can be taken over with social engineering. Unless it's the Stellar Account Viewer or Laboratory, steer clear.
Use a hardware wallet
Using a hardware wallet like the Ledger Nano S is the safest way to transact on the Stellar network. If you cannot afford a Ledger Nano S, here's your best alternative.
Exchanges are not wallets
Never use exchanges as longterm storage for assets. Use exchanges to exchange, then transfer your tokens to safety. They are centralized startups prone to attack or shutdowns.
The maximum amount of time I have left currency - crypto or fiat - on an exchange is 15 minutes...I don't trust them to hold money. I don't trust banks to hold money; how am i going to trust a two year old startup that has six employees.
- Andreas Antonopoulos, “Hot vs. cold wallets”
Create a cold and a hot wallet
To minimize the risk of complete loss of your lumens, store the majority in a cold wallet and use a hot wallet for your regular transactions. Learn more about cold and hot wallets here.