So this guide structure will be more of a step by step, so if you have any questions let me know!
1. The Setup
A. At The beginning of the game you want to setup some tier 1 Archers (Skeletons) in the middle. Start with 3-5, and move to fill the middle row.
B. Start placing some Slime's every 2 blocks where the mobs start from, and on the corner of the first turn. 10-15
C. Place Magma Cube's in between each of the slime blocks. 10-15
You will need to upgrade these units as the game progresses, but shouldn't be your main concern.

2. Game Plan
A. You want to Buy Mobs as often as you can. This will increase your gold count every 10 seconds.
B. If you take a quick look at the mobs for sale you will see a couple things.
1. Some mobs will give you more income if you buy more of them rather than the next tier up.
2. Some of the more expensive mobs will not give you any extra income at all and provide no personal benefit.
3. The mobs you can buy will change based off how far the game is, keep this in mind as you progress through the game.
C. Save up enough income so you can Easily make 150K-250K+ in the span of 30 seconds. (3 income intervals)
D. After you have about 500K+ your main focus will be to spam Ghast. You want about 7-10 Ghast on the board at all times.
E. When Step D has been Achieved you Can start throwing in some other mobs who aren't attacked by splash damage and move Fast. (Ocelot Is a good)

That's the Guide
If you found this useful or of value and feel like giving a reaction or comment that would be very appreciated
If you have any questions be sure to leave them down below and I'll reply as soon as I can