Confused as to how you know what to look for

Hi guys, apologies if this isn't the right place to post this but I'm confused as to how people know what to look for when answering crosswords.

I've never really done crosswords but I've had a private eye subscription for the past 6 months or so and the crosswords still confuse me! Sometimes I can get one or two words but I've never managed to get close to solving all of them.

Are there any general tips/rules you guys would have to help me?