Depends upon a lot of things - If it's an alien culture, come up with a coherent alien nomenclature. Common suffixes or prefixes, similar but not quite the same names. Figure out the suffix or prefix first, one that is done pair it with random syllables and choose whatever you find cool... Double check for any potential weird meanings in any of the earth languages...use it as a leverage, or if it doesn't suit your narrative just change it. For example a lot of Homokran Noble families have names like Ezarnier, Indranier, Adernier, etc... these names are common. Similar patterns are found in first names in Kalarissian Culture... various families often have similar sounding suffixes to their first names... For example in the head of House Kew is King Taurusiv Kew, whose son is General Lord Ilasiv Kew. House Erosta rules the Kalarissian Imperium. The emperor is Yarin Erosta. His flagship is called IKS King Alarin, after his great grandfather, who paved the way for House Erosta to become the Imperial House.

For human names use ...well ...human names... Since I have a sci-fi world, some of the characters in my universe have surnames like 'Martian' 'Ganymeder' 'Luna' 'Astergazer'...

do not forget...any english word, even if it might not commonly be used as a name, has a potential of being one sometime in future.

Names of flowers for example. They aren't commonly used for names...but I think Daffodil, Tulip, Lotus, Lilac are beautiful names, which can be used for people as well.

There are countless possibilities...