This is the most obvious one, you need your player in the correct position to gain higher chemistry.
Considering this, if your not too bothered about having the shiny green chemistry or don't want to spend as much money, here are 2 useful tips;

A. Spending less - If your looking to buy a CM say Hamsik from Napoli, as a CM you would be looking to spend around 5K for a decent formation. Although if your not bothered about having shiny green and one chemistry point, you could buy him as a CAM for around 1K, here you can see you've saved drastically and his position will still be green.

B. A different style - If, like me, you like to have decent paced CB's and struggle to find them for the right price, here's something you might consider; Say for example you wanted Ramires from Chelsea but you needed a CB, simply putting him as a CB as a CM wouldn't do, he wouldn't like his position and you would lose out on vital chemistry points. So what if you bought him as a CDM? Well he would have a green position so you would gain chemistry points and you would have yourself a fast paced CB without losing out on major Chemistry!

Okay so formation is really important to having good chemistry, but you don't have to buy the player in the formation you use to have good chemistry. Buying a whole team in 4-3-3 can prove very expensive! Here are 3 useful tips for getting good chemistry for less;

A. Goalkeeper and Defense - Say you use any formation beginning with a 4, like 4-4-2, 4-3-3, 4-1-2-1-2, 4-3-2-1 etc. To get shiny green chemistry you would have to buy the formation you use, but if you will settle for green formation then you can buy any one of that player as long as it begins with a 4! Same for the 3's and same for the 5's!

B. Midfielders - Personally i use a 4-3-3 formation and anyone who uses it will know its an expensive one! CM is the most expensive position to buy because the only formations that suit 4-3-3 are 4-3-3, 4-3-2-1 and 4-3-1-2 (for some reason 5-3-2 doesn't work),so since there's only 3 i haven't got much selection. If you use 4-4-2 you could use 3-4-1-2, 3-4-2-1, 4-4-2 and 4-4-1-1, this is slightly less expensive as you have more selection. So basically, if you don't mind about shiny green formation, as long as you buy a midfielder with the same 2nd formation, you can save!

C. Forwards - This is the easiest one for a 4-3-3 formation as there are so many to choose from! For a green formation i can buy 3-4-1-2, 3-4-2-1, 4-3-1-2, 4-3-2-1, 4-3-3 or 5-2-2-1! i have alot of selection and therefore more chance to save! If you use 442 you can use 3-4-1-2, 4-3-1-2, 4-4-2 or 5-3-2!

These are simple, buy a whole team from one league and they will all have green links to each other, buying players from the same club will create a shiny green link between them. As well as this buying players from the same nationality and league will also create a shiny green link between each other. The connection here is that to get a green link you will need either the same league or the same nationality and to get a shiny green link you need 2 together league and nationality or club (which is obviously league and club).

A manager can be a huge factor in gaining higher chemistry! Simply adding a random manager wont do much for your club but if you buy a manager with the same formation as you use you will get at least an extra 10 chemistry! The maximum a manager can give is 20, 1 point on top of the correct formation for him being the same nationality as a player in your starting 11, get 10 players with the same nationality as your manager and you have yourself 20 points just from your manager right there!