Strategy for Promoting Books in a Series #IndieAuthors #Marketing

As an Indie author, I appreciate free promotion. But, how well does it work? I summarize a strategy for a standalone novel in this previous post: http://auroraspringer.blogspot.com/2015/10/can-free-promotions-help-indie-authors.html
This month, I tested a strategy for promoting the three books in my Grand Master’s Trilogy. Using free sites only, I promoted Book 2 FREE from April 1-5thwith Book 1 set at 99c.  
Grand Master’s Pawn: http://www.amazon.com/dp/B00TP1N5PMGrand Master’s Game: http://www.amazon.com/dp/B0104OFJJ8 Grand Master’s Mate: http://www.amazon.com/dp/B018EHAA7S
Listed on the Following Siteshttp://bookangel.co.uk/submit-your-bookhttp://askdavid.com/free-ebook-promotionbookscream.com bookhearts.com  for 4/1/16bookpraiser.comhttp://theereadercafe.com/promote-your-books/http://www.freebooksy.com/editorial-submissions/  free99books.comEbooklister  bookbraghttp://www.frugal-freebies.com/p/submit-freebie.htmlBookhippo (unlikely since only 1 review in UK)Bookzio (tried)Readersgazette Patty Jansen’s Promo (Science Fiction, Fantasy & Horror) for April 2-3 (pattyjansen.com/promo)
Ranking : Book 2, Grand Master’s Game, hit top ranks of #2 FREE in First Contact and Space Exploration subcategories on Amazon at different times on the second day of the promotion. Amazon Best Sellers Rank:#502 Free in Kindle Store (See Top 100 Free in Kindle Store) #2 in Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > Space Exploration #3 in Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > First Contact #3 in Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Fantasy > Superhero  Amazon Best Sellers Rank:#452 Free in Kindle Store (See Top 100 Free in Kindle Store) #2 in Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > First Contact It reached the Amazon Best Sellers Rank of #388 Free in Kindle Store. Amazon Best Sellers Rank:#388 Free in Kindle Store (See Top 100 Free in Kindle Store) #4 in Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > First Contact   Book 1 Grand Master’s Pawn(99c) showed the best rankings of:Amazon Best Sellers Rank:#14,630 Paid in Kindle Store (See Top 100 Paid in Kindle Store) #101 in Books > Science Fiction & Fantasy > Fantasy > Superheroes #103 in Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Fantasy > Superhero #149 in Kindle Store > Kindle eBooks > Science Fiction & Fantasy > Science Fiction > First Contact
Here are the results: Sales over April 1-5th Book 2: A total of 1796 FREE copies given away.Book 1: 47 sold at $0.99Book 3: 8 sold at $2.99 Profit (All ROI) = $31 plus KU reads and continued sales over the next few days
Would I do it again? Yes! This free promotion worked better than the paid one I ran in earlier this year and the books achieved temporary prominence after weeks of little action. 
Thoughts: The boost is temporary.Discounting to 99c helps to track the results and brings in more readers. What strategy works for you?  
Secret Weapons I acknowledge help with tweets and retweets from the members of the eNovelAuthorsatWork group. and also cross-promotion by authors in Patty Jansen's Promo.