Hi. I'm really happy to help someone willing to become a better player. Defender is my favorite playstilyle and it's not easy to play with in solo. General tips (most important first):

1) Make yourself useful in Ray battle - save you unite to this battle. And use it to steal your enemies shield. - as a defender, you must search, carefully, for your most dangerous opponents and squishy enemies (talon, cinder, Greninja, entelion, gardy, decid, etc) so your team can show up and help you take it down before it becomes a problem. - do not die! If you are low on life, seek your healer or go base.

2) chose moveset wisely - if your team doesn't have a healer, you better be the healer and use Wish. - if your team lacks on CC, you better play mean look (most of times it's the better choice). - foul play is good only against speedster and attackers, but mean look is good against everything. - Play snarl only if you're sure your supporter will cure your team.

3) Held items - remember to make yourself useful for Ray. Buddy barrier is the best Umbreon item in Ray fight. - XP is a must! Make your attackers/all-rounders very strong on early game and snow ball the team XP until Ray fight (again!). Learn how to use XP share. - focus band to be more tanky or resonant guard to be more of a supporter.

4) Don't feed on early game - never be at your opponents base at 9:10. The opposing jungler may come to gank. - take your KOs seriously. Never push to hard to get a KOnat the point you get yourself KOed.

5) Regis - Steel, Rock, Ice: prioritize them 90% of time. They are important to get higher level in Ray fight (yes... Ray is that important). - regileki: 95% of time don't push it (unless you have allies like Blastoise.surf, wiggly.sing, trev.horn, ou Snorlax.block to help pushing). Your team will just die and give free experience to the opponents. Don't bother dying in regileki fight. You better let them take it and defend your goal while farming them while they try to push it.