Just don't spend more than what you can afford. Sometimes a couple of cents are enough to be on the top list in the promoted tab on ​tags that don't get much traffic right now, but are slowly growing. I'm not stating that you will get your investment back, so just put a little, @promoted will compensate you also a little. But to make a successful​ post takes more than just promoting and paying for a whale vote.
Steem on!