Find a good source of recommendations that matches your taste.
Find a blogger, columnist, or critic with the same tastes as you. Stephen King has a column in Entertainment Weekly magazine that I like. His movie and television recommendations are usually pretty good, although his music is weird and random.
When you should (and should not) trust the critics.
Many people do not trust critics and think they are elitist and out of touch with true entertainment. I mostly disagree with this, but there is a sliver of truth to it. Movies with a political or social message critics agree with will usually receive stellar reviews regardless of entertainment value. Most critics seem to dislike sentimental or moralistic movies. If the movie covers topics like religion, sex, politics, foreign affairs or family, it might be wise to get an opinion apart from them, depending on your own views and tastes, of course. Just look at the topic of the movie before you trust reviews. But this bias does not exist in all critics. This is a generalization that holds some truth, but should be taken with a grain of salt. My rule of thumb with critics is that when they love a movie, I may or may not love it too. But if they trash a movie almost unanimously, I take it as a sign that I will almost definitely hate it. They know when something is truly awful.
Why critics are actually worth listening to.
If you do not pay attention to the consensus of critics, remember that they see a lot of movies and love film. Their tastes have been refined through years of sitting through and analyzing hundreds of movies. Many critics see the movie they review twice. The first time, they just watch it for entertainment value like anyone else. The second time they look at more technical aspects, such as camera work and acting. If they hated a movie you loved, it might be because they have seen three movies a lot like it that were better. Experience is helpful even with movies.
Ask around your own circle
Ask your friends and family. They know you and what you like. You also know them and what they like. If someone in your family loves a movie, you might want to see it just because it is dear to him or her.
User reviews are a mixed bag usually not worth digging into.
Do not read user reviews on sites. They are rarely useful and are usually contradictory. Critics either love a movie or hate it. The user ratings tend to be somewhere in the middle or high for every movie. However bad the movie is, there is a chance that someone, somewhere online is going to love it. For example, my sister loved the movie Hitman, even though it has a very low rating on RottenTomatoes. If you are going to trust other people, make sure they are the right people and not just random teenagers posting rants or raves.
Do not be snooty. Follow the big crowds.
But you can believe the buzz. If a movie is extremely popular and nearly everyone you meet says it is good, you should probably check it out. Examples of this include Titanic and the Harry Potter book series. Even if you end up hating something really popular, you will not be able to discuss it if you do not check it out yourself. If everyone else loved it, chances are, there is a reason for that. You will probably enjoy it too, or at least find something you love to hate and rail against. I found that with the Twilight movie. I thought it was terrible, but I had tons of fun mocking it. It is fun to mock something that everyone else has seen so they will know what you are talking about when you make jokes.