Today's pro player has been using this deck inside the TOP 10 in the world, every card inside this deck has strong synergy with another units which is what makes it so strong. I recommend playing aggressive and keeping up the pressure throughout the match. Heal spirit can be used alongside the royal hogs when you know the opponents log is out of cycle. You might also need to bait out spells like fireball before pressuring with the hog. Use the two spells to help support your units, for example the barb barrel can be used to act as a mini tank for other units inside your deck to help shut down swamr cards. The fireball can deal a lot of tower damage so you should aim to get tower chip as well as hitting the opponent's units.
Mega knights unique enter the arena ability makes him a good defensive option against, royal hogs, swarm units, bait cards and bridge spam units. Against high DPS units he will need support from the musketeer or fisherman which can be used to pulls units away from him. Try not to use him too much in single elixir unless you need to use him on defence. In double elixir you can counter push behind him with the royal hogs.
Musketeer can offer a lot of defensive value if you use her correctly, protect her from the opponens troops to keep her alive as long as possible and potentially bait out a spell from your opponent. She is also your main defence against air units like lava hound or balloon, try to counter push with her after a successful defence by using her as a support card.
Hogs are your main win condition inside this deck. You should mainly use them all in the same lane unless you know your opponent has a couple of counters to these guys, for example mega knight, valkyrie, wizard or bomb tower, try to bait out their key counters and then use these guys on offence. Try to support them with your heal spirit and spells while having the mega knight tanking tower damage.
Early game try to activate your king tower at the earliest opportunity by using your fisherman. You should also aim to build a good elixir advantage while learning what deck your opponent is playing and what their main counters to your deck are. You can pressure with the hogs if you know your opponent is low on elixir or they've just used their only counter to your royal hogs.
In double elixir you can start to use your mega knight more on offence as well as using your spells to help support your pushes. Remember to protect the musketeer and keep her alive as long as possible, it's still important to bait out counters to your hogs. If you have a strong counter push in one lane but you know your opponent can defend it then try pressuring opposite lane with your hogs and heal spirit combo.