Edward,
remember GPA is only a portion of the picture.
do
1. Speak to your Cadre. If you haven't found it online already, your Cadre should be able to guide you to the FY18 OML.
2. If you hunt around a little, you can find a break down of where cadets placed on the OML versus branching. That will give you a rough target to plan around.
3. Expect things to change, what the OML ranking system today can/may/will change in the next few years (The new APFT may be interesting for some).
4. GPA is only a portion of the ranking. Once you understand the OML, you will see that there are some "bonus" points for certain degrees that help.
5. Plan around that target OML score and give yourself a buffer (Murphy's Law).
6. Remember the OML GPA calculation is based on your junior year GPA. So with engineering be very careful about course overload. The first two years are more than challenging.
7. Keep your eye on the ball. If you are at an ABET accredited school stay on the path towards gaining a license.
Also recommend you speak to your cadre clearly about engineering degrees. Many require a 5th year if you co-op. Your Cadre can guide you around that hurdle if needed. My DS received very good information from one of the few other cadets that was also an engineering major. This included some advice about delaying a class to the senior year.
My DS and I just went through this discussion in the last few weeks. Having a copy of the OML was useful to discuss time management and relative benefits of activities. Few engineering majors have the time for a language, but there are ways around that and other ways to increase your score.
Good luck from a Civil/Mech...(yes both)...