Yeah, I think Socal has the key point right. It's a little more complicated that this, but for a beginner ref working at grassroots level, working off the basis of ball first = no foul and player first = foul will get you 95% of the way in judging on-the-ground challenges.
The remaining 5% are the ones where the level of force/risk is so high that it needs to be a foul (and probably a card) regardless of contact - the sign for those is that if you're sucking air in through your teeth at a challenge, you probably need to be blowing that air out into your whistle!
For upper-body fouls, don't be fooled by the shouts of "hands in the back ref" that you'll hear a lot of. A player using their hands to judge where an opponent is while they watch the ball is fully legal - what you're looking for as a ref is a clear pushing/pulling motion (straightening/bending of the elbow), or a holding offence, which will either result in the shirt stretching or a limb being clearly grabbed.
For all of these upper-body offences in particular, being in a side-on position makes it so much easier to judge. At an absolute minimum, you should work on being side-on for any long goal kicks or free kicks taken by the GK, as those will be static set pieces and you can position yourself correctly before allowing play to start. Remember as well, if the ball is being crossed in from wide or a corner, "side on" is actually likely to be vertically up the pitch from the drop zone, so adjust your position accordingly.
Final point - when you make a decision, make it with confidence. I wonder why it is you feel your foul recognition isn't good? If it's because you're getting a lot of "negative feedback" from players, it could well be that you're making good calls but not portraying confidence in the decision?
New referees will often give away a lack of confidence by doing a half-hearted whistle or point when they're not sure about a call. But for any experienced referee it's the opposite - you'll notice it's always the 50/50 calls that get a big strong whistle, a firm direction signal and in some cases, high energy running to the spot of the foul. Again, for a new referee, I'd recommend on trying to get a consistent decision-making style. With a bit more experience you can allow variation, but the most important thing is portraying confidence in every decision, even if you don't feel it.