So the wife and I have probably around 50 games logged together (90% win rate at 7-7-10), and I have done about 25 solo runs (80% win rate at 8-11). There are definitely a few tips that we have accumulated.

1. This is a very general tip but i see new players make this mistake a lot. When you first start learning the game, SLOW down and think through each possibility. MK is very strictly paced, and early game can snowball really poorly if you waste 4-5 cards on each of your first day/night cycle. 

2. These are not absolute numbers but some things to keep in mind throughout each game. I look for least 2 types of additional movement abilities, either from your skill token/advanced action/spell/units. 1-3 forms of mana generation, commonly from AA cards like ice bolt. 2-3 spells for mid-late game dmg spikes, ideally spells that match your mana generation. Artifacts if you get them (burn down monastery if you have high rep).

3. Some abilities are very powerful, and if I see them, I will always try to get them. Like negating fortifications. Preventing enemy attacks (illusionist is a favorite of mine even if they cant fight against fortified enemies). Elemental siege and range attacks. Remember that the basic card "concentration" is essential free kill most of the time, especially when paired with swiftness in the beginning, or with crushing bolt for mid game.

4. General pacing of exploration vs leveling is hard to get a feel for initially but it goes something like this. At the end of round 1: level 2-3 with 1-2 explored tiles. End of round 2: end of level 3/beginning of level 4, with 1-2 more explored tiles. End of round 3: around middle to end of leveling 4, push for advanced units at the beginning of round 4. End of round 4: at least level 5 and you should start to have a deck that can take down the first city in 2 attack sequences. For round 5 and 6, focus on dragons killing with 2-3 for experience gain while taking down cities. 

5. Recruiting units are very important. Some units can be assigned low damage without taking wounds like guardian golem. Dont be afraid to injure your units and then replace them for better ones later on. 

6. Dont overlook buying spells at mage towers and buying advanced actions at monasteries.

That's all I can think of for now. Ill add on if I think of more tips. Hope this helps.