First of all , i'd start doing this https://www.mmobomb.com/giveaway/s4-league-gift-keys so you can get some perm items.
Then , what you need to do is find 3 weapons and a skill that you feel confortable playing with.
SAVE YOUR PEN (this is a must) and only buy Weapon and Set capsules when you have at least 300k pen and a booster x2 (from my experience this work , others might have different experiences).
You can try the shop but to be honest i'm not a big fan of it.
And at last , watch some Youtube videos so you can see some tricks and tips to help you get better overall.
Forgot to say that when you have 3 weps perm that you like , start investing on chips.