To advance eco-driving skills in hybrid electric vehicle (HEV) drivers, and thus facilitate fuel efficient driving behavior, a set of 15 ecodriving-tips was developed and tested. In part 1, car owner manuals and telephone interviews with HEV expert ecodrivers were analyzed to extract ecodriving-related statements. As the owner manual statements were too generic to be used for the content generation of the ecodriving-tips, only their style was used for formulation purposes at a later stage. The interview statements were used for the content generation, and thus condensed into a concise set of 15 ecodriving-tips. This set was then formulated in three versions. Version 1 was based on the “no context, no details” formulation style extracted from the owner manuals. Version 2 and 3 were psychologically-grounded: Version 2 was based on the concept of implementation intentions, and therefore contained “if-then-plans”. For Version 3, these “if-then-plans” were coupled with technical explanations to additionally target the improvement of drivers’ mental models. Eventually, to ensure technical correctness, all three versions were reviewed by a HEV powertrain expert. In part 2, a longitudinal field study with two points of measurement was conducted to test the three versions in a randomized controlled design. For this, HEV drivers were recruited and randomly assigned to one of three groups. At baseline, each group received and evaluated a different version of the ecodriving-tips and was then asked to test the tips over the next 31 days. At follow-up, all groups, again, evaluated the ecodriving-tips. At both points of measurement self-reported fuel consumption was assessed. To sum up, 81 participants evaluated the tips as largely positive, both at baseline and follow-up. Furthermore, participants who received Version 3 of the ecodriving-tips (implementation intentions and technical explanations) significantly reduced their fuel consumption by 4% on average over time.