If you want to practice Mandarin well, you must first make sure that the phonetic symbols of your pinyin are correct. If you can't tell the difference between pool and wisdom, what you say may mean two things in other people's ears. So be sure to correct your pronunciation of phonetic symbols.
You can usually listen to what others say. For example, news broadcast and weather forecast are very accurate in Mandarin. If you want to practice Mandarin well, you might as well listen to what others say first, starting with imitation.
Besides listening, you should read more books. Usually, you can read some books or newspapers to read the whole sentence smoothly, so that the spoken Mandarin will be standard and fluent. If you want to improve Putonghua, you can also say some jingles, such as "800 pacesetters March to the north slope, 800 artillery guns to the north slope" and so on. Besides listening and reading, the most important thing is to communicate with others in Mandarin. If you can't communicate freely, no matter how good Mandarin is, it's still zero. Only by communicating with people naturally can we practice Mandarin well.
There are also Putonghua training classes, and there are also software for learning Putonghua on mobile phones.