As I demonstrated here (
click),
Sindarin mostly requires expert level knowledge on the historical phonetic development rules of the language to be able to form accurate names. Most attempts by beginners would yield inaccurate results, unless by chance they stumble upon a combination that does not require any change, which is rare. To "luck out" like that, a trick would be to use words which begin with vowels for non-initial elements, for example using
adan "Man (
race)" with
mell "beloved" as
Melladan "Beloved-Man" would be a straightforward combination with no change. But this trick does not guarantee that the results will be accurate, it only increases one's chances. For example, using
cair "ship" as the initial element should instead yield
Ceiradan "Ship-Man", because "ai" can only appear in the final syllables of polysyllabic words (e.g.
erain) or in monosyllabic words (e.g.
cair). And a more archaic form would be
Ciriadan (because
cair comes from ancient
KIRjā > kirja > kerja > keria > keri > keir > kair, and most of these changes depend on the word's having no following element, thus the modern compound
Ceiradan is sort of a reformation which removes only the latest "(final) ei>ai" rule).
Quenya is much safer with regard to its phonetic rules, but they are not non-existent. For example
ar(a-) "noble" and
cáno "lord" would simply be
Arcáno or
Aracáno "Noble Lord", but an element like
ñolmo from primitive √ÑGOL (note: "ñ" stands for /ŋ/ in
Tolkien's usage) would become
Argolmo (note: "g" in Quenya can only survive after "r & l", and only if it comes from "ñg") or
Arañgolmo. But cases like this are rarer in Quenya, thus it is easier to form accurate names in it without prior knowledge.
Another thing to keep in mind is that
Elvish names are never made up of just one element (i.e. adjective or noun). As Tolkien says here:
The mere names of things, such as 'hill, river, tree', and especially of unique things, as 'sun', were not used, at any rate without differentiation: [...]
for that would imply some kind of total equation or identity. An Elf (or Man) would not be called Anar
'Sun' even to depict great glory or radiant vigour. [...]
But an Elf or Man could be called Anárion, Anardil [etc.] [PE21/86]
So at least two elements, either another adjective/noun or some masculine/feminine suffix, are needed. Also note that Tolkien's example Q.
Anárion shows another instance wherein the phonetic rules of Quenya seemingly made changes to the isolated
Anar form, but this word was actually A-NĀR (note: "ā" = long a) and it only lost its "ā" due to being final, but it is not final with
Anárion and so it remains, meanwhile
Anardil has a short "a" because the following consonant cluster "-rd- shortened it. As a final note, there is no attested Sindarin name with more than four syllables, so
brevity is the soul of wit and all that.