My "successful (promotion) strategy" was to only go after domains that were likely to "sell themselves".
Not today. Not in 90 days. Maybe in 5, 10, 20 years.
When you do your homework - market research and analysis - you get results.
Add in patience, cash flow management, and having a sound understanding of market forces and you might land a few decent sales.
If you're after "get rich quick" domains odds are you will end up losing money. Forget "promotional strategies" and wrap your head around acquiring domains that, based on domain intelligence, are likely to sell themselves. For substantial money, which may also mean spending $$$$ to $$,$$$ to acquire the domain (or a lot more if you have the $ and the ability to wait things out, i.e., don't need an immediate turn around).
Do NOT look to acquire domains to be sold "to the aftermarket", that is, resellers. That' makes you the loser or the fool, as anyone buyer from domains for re-sale look to acquire domains they can sell for 10x, 20x, 100x your sale price. It takes a savvy domainer to acquire domains with a strategy of selling for 2-5Xs their acquisition cost and by that I mean $1000 -> $3,000, $4,000, etc. Very few people are qualified to "work that market".
So, you ask "what are currently your most successful strategies to promote your domains?"
Don't buy junk. Don't buy on impulse. Don't follow the crowd or endeavor to copy others. Don't believe everything you read. Don't spend money you need to recover quickly. Don't believe there is a "promotional strategy" that will save you from your bad decisions.
Buy ONLY domains that will promote themselves OR that you are prepared to and will enjoy developing OR that you have money to burn on poorly fashioned speculation.