Hey there :)
I've never really experienced anything serious in the other planes, though some of the creatures you meet tend to not like humans very much. Humans have a bad habit of screwing other creatures over, most notably not following up on promises, so many creatures, especially dragons and many Fae, are wary of humans. You have to be humble and polite when talking to creatures on the astral and never make promises you can't keep.
I ask a guardian or God to come with me when I astral travel. I also carry a 'whapping stick' with me juuuust in case I need it. In 20 years I've needed it only once and that was because a ghost in my home was making a pest of itself.
I was astral traveling decently the first year I started practicing. I generally only visit the Gods on the edges of the universe, but when I have traveled elsewhere, I've never had any problems.