To get things back under control in Game 1, the Cavaliers absolutely need to play better defense on Kevin Durant. Durant is a legend in the making, but the Cavs are certainly capable of doing a better job guarding him.
In his postgame comments to Doris Burke, Durant included: "[...] And I might not be able to get those shots next game, but if I do, [...] I've got to continue to knock them down [...]."
Courtesy of the NBA, below is a video of some of Durant's highlights from Game 1. I have added notes about each play. Of the 16 featured plays, the Cavs played the appropriate defense once and had no options in 2 others; they messed up on the other 13 plays.
1. 0:12 - Durant driving layup: soft double-team; LeBron and Love flatfooted
2. 0:17 - Durant alley-oop from Green: LeBron overplayed Durant's cut towards a fake screen
3. 0:25 - Durant drive and assist to Pachulia off a pick-and-roll: double-team; LeBron flatfooted, Love overplayed
*4. 0:35 - Durant jumpshot from Iguodala off a Curry screen: *LeBron defended correctly; nicely made shot
5. 0:45 - Curry to Durant for a dunk in transition: LeBron flatfooted
6. 0:51 - Durant pass from Curry, driving assist to McGee for a dunk: triple-team on Curry at the top of the three-point arc; rotations off; LeBron had to cover for JR/Kyrie/TT; JR and D-Will did not react; in general, smaller/weaker defensive lineup hurt the Cavs
7. 1:01 - Durant coast-to-coast dunk: Kyrie didn't stop the ball; Korver/LeBron didn't cover up
8. 1:09 - Livingston to Durant for a dunk: LeBron overplayed double-team on the ball; Love didn't cover up
9. 1:16 - Curry to Durant, driving layup from three-point arc elbow: Shumpert flatfooted and poor angling; Love late with help; Korver tried to cover up
10. 1:25 - Klay steal to Durant dunk: JR should've covered the ball/KD but went to cover Curry; Shumpert didn't try to cover up
11. 1:53 - Curry to Durant short jumpshot at left block: Kyrie mismatch; LeBron didn't double-team
^12. 2:03 - Curry/Green double-team on JR and steal; Green to Curry to Klay to Durant for 3 on left wing: LeBron and TT tried; ^great fastbreak
13. 2:15 - Durant fastbreak to Curry for 3 at left elbow: Love didn't challenge Durant before halfcourt (could've cut him off and made him change directions); Irving should've been guarding Curry instead of dropping towards the basket to cover the low post
14. 2:23 - screen by McAdoo at top of three-point arc, Durant jumpshot at right elbow of key/free-throw line: Jefferson overplayed, slipped, and fell
^15. 2:32 - LeBron missed 3, Durant outlet to Green for dunk: ^great execution; D-Will too short, not able to deflect ball, not a good defender in general
16. 2:42 - Curry steal (LeBron trying to break a triple-team in transition), Curry to Durant for a 3 on the right elbow: JR misplayed the double-team, should've showed double-team and went right to covering KD
2) Better passing.
Better passing, more movement, and smarter ballhandling are all necessary in Game 2. The Cavs forced a lot of passes into coverage, with Kyrie and LeBron trying too hard to attack double-teams and triple-teams off the dribble. The Warriors finished with 12 steals and 27 fastbreak points to the Cavs' zero steals and 9 fastbreak points.
Below is a video of the Cavs' turnovers from Game 1. I disagreed with one charging call, but otherwise, the Cavs did a poor job in most of these plays.
3) Better rebounding.
The Cavs actually had a 59-50 edge on rebounding. However, the Warriors had 14 offensive rebounds compared to the Cavs' 15 offensive rebounds, outscoring the Cavs on second-chance points, 18-13. The Warriors attempted 106 shots vs. the Cavs' 86 attempts. The Warriors had 56 points in the paint to the Cavs' 30 points in the paint.
4) Bench slumping players; next man up.
The Cavs played well in the 1st quarter until the benches started to substitute into the game. The Warriors' had their big four each play at least 34 minutes with their bench thoroughly outplaying the Cavalier bench. As Coach Lue has shown in the past, he is willing to bench struggling players. He sat Shumpert in the playoff opener this year. He took Delly out in the middle of the Finals last year. He sat out Frye for most of the Finals last year and sat Mozgov for most of the playoffs.
Defense wins championships. This year, he may need to sit D-Will, Korver, Shumpert, and at times TT. As Golden State runs a lot of motion screens with lots of passing, they need guys who can switch and cover Durant and Green. This means Jefferson, Derrick Williams, and Dahntay Jones may get the call ahead of the aforementioned players.