Yeast starter kit and stir plate. Game changer.
When I started brewing, I kinda felt that yeast starters where only an advanced brewing technique and were likely overstated in their need.
After two IPA brews, with an OG of 1.070 and attenuating down to only 1.016 and 1.017, and being overly sweet, I made the purchase and started trying to learn about yeast and proper pitching.
My last two IPA's that were also 1.070 OG, but this time I made 2L starters. They ended up attenuating down to 1.008 and 1.010. Same yeast, same ferm chamber settings.
No more overly sweet beer!