Ruiz vs Joshua II
Double jab, right hand
I don't think Joshua should be first with the single jab, because Ruiz is too good a counter puncher, is too good at cutting distance, he doesn't have as good a counter overhand right as Povetkin, but he still has good head movement, and I think being first with the single jab is an ineffective tactic against Ruiz. The counter jab is a good weapon for Joshua, because it stops Ruiz in his tracks, and if Joshua can land it, round after round, everytime Ruiz tries to get on the inside, that will take more out of Ruiz. The double jab is a great weapon for Joshua, because it gets Ruiz in position, sets up the right hand, and even if Joshua doesn't follow it up with the right hand, the jab still scores points, and the second jab stops Ruiz capitalising on the opening which the first jab gives him. The long right hand is definitely the best power shot for Joshua, because while it does damage, it is a shot thrown from a safe distance for Joshua, and range is very important for him.
Use your feet
Joshua's best defence is definitely the use of his legs, because it's hard to use head movement and blocking abilities against Ruiz, who is fast, accurate, throws combinations, but he has slow feet, so the best way to defend against Ruiz is to disallow him getting into his punching range. It's important that Joshua doesn't go back in a straight line, because if he does that, Ruiz can walk him down, he'll hit a dead end, and if he can't get off the ropes, all he can do is tie up or try to fight in the pocket, I think neither are good tactics for him, he can't out fight Ruiz in Ruiz's punching range, and I think Ruiz can do damage as he works out of a clinch. Joshua needs lateral movement, needs to pivot to get out of range and avoid exchanges.
Ruiz's counter left hook was what changed the fight the first time, he hit Joshua high on the head, hurt him bad. This time, Joshua is likely to hold the phone on his right side, meaning his right hand will be high, he can't realistically keep the hand up for 36 minutes, because he needs to throw his right hand, but aside from being patient, waiting for the opening, Ruiz should go to the body with the left hook, it won't be easy to get past Joshua's jab, but if he moves to his left slightly, he can avoid the jab, step in and land the left hook to the body. Joshua has a long reach, but if he holds the phone, that will bring his elbow up slightly, give Ruiz an opening to the body. Ruiz might be wise to set up the left hook to the body by throwing the lead left hook to the head, that will take Joshua's mind away from the body, and with Ruiz's head movement, I don't think Joshua can land the single right hand as Ruiz comes in.
Make him work
In the early rounds, whether he wins them or not, Ruiz can't let Joshua control the pace, and if he holds off, tries to be clever, tries to out box Joshua, I think that won't work, and it will allow Joshua to work at his own pace, and even if he tries to be a defensive puncher, backs up and tries to fire a counter off the back foot as Joshua attacks, that's a bad tactic, because Joshua won't take that bait. Ruiz has to apply educated pressure, can't get frustrated about struggling with the range, has to make Joshua exert his legs, because the more Joshua has to use his legs, the less mobile he'll be down the stretch, and even though it won't take away Joshua's jab, the jab will lose speed and snap if he's been made to work hard, round after round. If Joshua's feet slow down in the second half, and Ruiz can get past his weaker jab, Ruiz can fight his fight, and that's not a fight Joshua can win.
From what I understand, Ruiz and Joshua will both be lighter in the rematch. I think being lighter will be a big help to Joshua, it will benefit his stamina, mobility, and he won't lose power, he will be slightly less strong, but overpowering and out hustling Ruiz shouldn't be part of his game plan, so it's worth the sacrifice in strength, for better stamina. Ruiz, in terms of hand speed, stamina, overall conditioning, was fine last time, the way he looks means nothing, but if he loses a small amount of weight, I think that will benefit him if anything, because slow feet were a problem for him in the first fight, so if he is lighter this time, and that increases his foot speed, he can get into his punching range more quickly.