Learning the art of critiquing, in my opinion, is an important part of the writing process. Examining another writer's story with an eye for what's working, what isn't and why can help you understand the craft on a deeper level. It does take time to read and critique, but it's time well spent. especially if you're receiving a return critique.
It can be difficult, however, when you read something you really don't like. For me, this is the hardest part. I know what it's like to pour your time and soul into a project. I don't want to hear at the end that it amounts to a pile of rotten beans. Regardless, if it's the truth, it's the kindest critique partners that will come out and say it. It would be much worse to let those smelly legumes out into the world with your name written all over them for everyone to see. A harsh critique is often a blessing. I've come to love people's opinions about my work, both good and bad. It's all helpful. When your main objective is to grow as a writer, you learn to set your ego aside and focus on craft.
When giving a critique, I like to start by telling the author what I liked about their story/writing. Then when I get to the harsh stuff, the stuff that didn't sit well with me, it's not as painful. Hopefully. Also, I always keep in mind my opinions are just that. Opinions. Mine. My way isn't the only way, and just because I don't like something doesn't mean it's wrong.
A critique is always an opinion. Get several people to read the same story, and you'll most likely get several contrasting views. If you get a bunch of people saying the same thing, that's when you know you need to make some changes, or if they all love it, leave it alone. It's usually not so clear, unfortunately. I've had one person tell me they hated something about my writing, and someone else say they love that very thing and that's what makes them like my work. You can't please all the people all the time. Best not to even try. When you get contrasting critiques, take them all into consideration, then decide whether or not you think the advise is worth applying.
One of the best articles I've ever read on giving a diplomatic critique was written by Andrew Burt
for Critters Writers Workshop. I'll add a link to the article here.