I skip the actual game play recommended changes as especially Hawkeye has brought up most of it already but concentrate on the coaches.
- revamp the bonus points/skill combinations: in case a coach offers two really good skills, as for example the all beloved TSI/MD combo he/she should reward less attribute points, at the same time less attractive combinations should get combined with the maximum of 50 points instead. Also look at some of the skill combos in general investing 15 points into S&V in order to unlock a trainer that gives "Longer, Better!" is odd, same goes for 15 points in DBL to get "Instant Rocket"
- reposition certain coaches; the previously mentioned Pei Jing Quah combo TSI/MD should be available only in case you invest the fast majority of your points in DBL (it should be one of the ultimate defensive combos), being able to get both skills, 15 attribute points on both forehand and backhand each and on top (up to) 12 points in OBL is simply way too good, so change the prerequisite to at least 14 or 15 DBL instead (on top of adjusting the attribute skills as written above).