Here are a few ways to avoid malware and viruses when downloading apps to your smartphone:

1. Download apps from legitimate app stores: Apple Store, Google Play, and Samsung Galaxy Store. While these platforms have review protocols that can detect and remove malicious apps, they are not perfect so caution is always important.
2. Pay attention to the permissions. Make sure you know which permissions are included in the app. Common permissions include access to: contacts, photo gallery, location, calendar, camera, browsing history, and more. Do you really want the app to have access to all of these? If not, maybe you don't really need the app.
3. Read the reviews on the app you are considering. While negative reviews are not always a red flag, it is good to be informed about possible issues.
4. Keep your operating system updated. Many of the OS updates include important security features that can prevent malicious software from infecting your phone.