I am a relative newb as well

When you're setting up tactics, really pay attention to player attributes and what it is you're asking them to do

I like to start building my formation from the middle by selecting my best defenders, holding mid (or miss), possibly creator in central attack, and of course a striker.

Your holding mods are stationary, providing support in defense and will often be your main ball winners spearheading a counter attack by quickly getting the ball to more effective playmakers.

So now you need to decide how your fullbacks will behave. Maybe you need them to provide overlapping support to create width in attack and open chances up for your centrally based attackers.

Last I'd look at my wings. Do I need defensive help? Then I'll opt for an ML and MR in a 442 or 4411. Can my holding mid(s) and fullbacks effectively win back possession without giving up my outlets for counters? Then I will have two IFs if I'm in a 4231x or two wingers on support duty in a 4123.

Basically, answer these questions:

Do you have a decent enough base defense set up to defend counters after losing possession?

Are you using your fullbacks and/or wide AMs in a way that they are giving your squad enough width in attack?

How freely do you want your CM(s) and/or AMC to operate in transition and the opposing third?