The best way for native Cantonese speakers to learn how to speak 普通話 is to install a mobile phone app "Microsoft Translator"
Open the app, tap the Mic button, configure the language as in the picture below.
Tab the Mic button, speak in Cantonese, the app will translate 廣東話 to 普通話.
Left swipe will show the Pinyin spelling with tone marks.
The app also translates the ultra colorful 廣東方言 into more formal language, e.g.
食饭 becomes 吃饭, 食嘢 becomes 吃东西, 睇乜嘢 becomes 看什么
番嚟 becomes 回来, 夜晚 becomes 晚上, 係唔係 becomes 是不是
攪掂 becomes 完成, 就咁 becomes 就这样, 晏昼 becomes 下午
好犀利 becomes 挺厉害, 伙记埋单 becomes 员工买单, 即刻 becomes 马上
发嬲 becomes 生气
"s"音: 上下前牙相貼。聲音從牙齒中間出 upper and lower front teeth touching; force air out between teeth similar to a snake hissing 類似蛇的嘶嘶聲
Ü 音: 女 (nǚ 3rd tone) 旅 (lǚ 3rd tone) 旅游 (lǚ yóu) 律师 (lǜ 4th tone shī) 利率 (li4 lǜ 4th tone) 绿色(lǜ 4th tone sè)
"r"音 特別難學: Tongue points up touching the roof of the mouth.
如 (ru 2nd tone) 入 (ru 4th tone) 入学 ru4xue2
人 (ren 2nd tone) 日 (ri 4th tone)
熱 (re 4th tone) 热水 (re4shui3) 肉 (rou 4th tone) 牛肉面 (niu2rou4mian4)
軟 (ruan 3rd tone) 软件 (ruan3jian4) 然 (ran 2nd tone) 然后 (ran2hou4)
容易 (rong 2nd tone yi 4th tone) 榮幸 (rong 2nd tone xing 4th tone)
Note 容 and 榮 are pronounced identically
湾 wan (1st tone wān) 湾仔 wān zǎi
玩 wan (2nd tone wán) 一起玩 yì qǐ wán
晚 wan (3rd tone wǎn) 晚安 wǎn ān
萬 wan (4th tone wàn) 一万块钱(一萬塊錢) yí wàn kuài qián