Show Don't Tell
All editors advise their authors to show, not tell. What this means is that, instead of writing long paragraphs of explanation or description, you should dramatise what happens or your characters’ traits. In other words, do not tell the reader that a particular character is vain or selfish, but show your audience that they behave in a vain or selfish way. Of course, as with all aspects of writing, there are not any absolute rules or correct ways of doing this because exposition and description can play useful roles in your narrative. You must decide what is right for your novel and the story you have to tell.
However, do bear in mind that extended explanation or description tends to be more difficult for your reader to absorb and also substantially slows the pace of the story. You may use either of them exactly for this purpose sometimes and it can be quite appropriate if you seek to vary the pace of your book. However, on occasions when the events or characters you are writing about are immediately important to your story, it will probably be more effective to show the action or behaviour to the reader.
This is true not only of explanation and character description but also physical description. There is nothing wrong with a short physical description of a person, object or setting, but it is often more effective to find a dramatic way of sharing the information with your reader. Perhaps you might have a character comment on another's physical appearance, or by dramatising how a character reacts to something or a setting as opposed to describing a house as neglected or in need of repair, your character might rub their fingers through flaking paintwork.
Take time now to review your first chapter and consider any long pieces of explanation or description and think about whether they need to be there. To this end, consider if they are vital to your story or whether you can dramatise them and make them more easily understood by your reader. Also, if you are describing a character, think about whether you can dramatise their behaviour or give an illustration of the qualities you are explaining to your reader. Equally, when you are making a description of the appearance of one of your characters, the setting or something being used in the story, find a more dramatic way to explain the information.
Go through your whole manuscript, using that first chapter as a template and follow the suggestions made in this and earlier chapters all the way through your book. It will take time and concentration, but it is imperative if your work is to be in as good shape as possible when you submit it for consideration by an agent or publisher.