What are the common features of "Elvish" conlangs?

Question

I want to create a fantasy world with Elves speaking their own language. In order to avoid unwanted associations with works of other authors, the Elves should speak a newly invented language. What features make a conlang sound "Elvish" in a fantasy setting, delineating it from languages of other races (like humans, dwarves, or orcs)?

My picture of Elves is heavily influenced by the works of Tolkien. The Elves are tall and strong humanoids with very long live-span living in the forests of my fantasy world. They are fond of arts and crafts and of poetry, but also engage in fights and wars when necessary.

Elves like these are a common race in genre fiction by many authors, and they also occur in genre based games (e.g., Dungeons and Dragons). They often have typical Elvish names, and some authors also invented some bits of Elvish languages for them. So I assume there are some common features for Elvish languages. What are they?

EDIT: In the meantime, this Wikipedia article has acquired a quite comprehensive list of Elvish languages.

Answer 1

One way to look at "elvish" features is to compare how different elvish languages look, and to take inspiration from that.

A look at the phonologies of a few elvish languages:

Quenya
(phonology from here)

         Labial Alveolar Palatal Velar Glottal
Nasal        m       n              ŋ
Stop       p b     t d            k g
Fricative  f v     s     (ç)      x     h
Trill                r
Semivowel (ʍ) w             j
Liquid               l

      Front Central Back
Close  i(ː)         u(ː)
C-Mid  eː           o:
O-Mid  ɛ            ɔ
Open         a(ː)

Sindarin
(phonology from here)

         Labial  Dental Alveolar Lateral Palatal Velar Uvular Glottal
Nasal        m       n                              ŋ
Stop       p b     t d                            k g
Fricative  f v     θ ð   s       ɬ                      χ      h
Trill               r
Approximant                          l       j    ʍ w

        Front Central Back
Close   i y             u
Near-C  ɪ               ʊ
O-Mid   ɛ               ɔ
Open          a

Some common denominators in Tolkien's Elvish: They all have distinction between voiced and unvoiced stops and (labial) fricatives, both have the somewhat /ʍ/ as a phoneme or allophone as well as /ŋ/, /x~χ/ and /h/. With vowels, they each have four vowel heights but nothing much in common beyond that. Allowed syllables seem to be (CC)V(CC) in Quenya (many more details at Wikipedia) and (C)V(C) in Sindarin, though I don't see that explicitly.

Pathfinder Elf Names
(names from here)

Male Names: Caladrel, Heldalel, Lanliss, Meirdrarel, Seldlon, Talathel, Variel, Zordlon.

Female Names: Amrunelara, Dardlara, Faunra, Jathal, Merisiel, Oparal, Soumral, Tessara, Yalandlara.

My interpretation of the names hints at some of these features: Only two nasals, voicing distinction, five vowels.

Allowed syllables: Apparently (C)V(CC) or (C)V(LC) where L is a liquid (l or r) or nasal

Dungeons & Dragons Elf Names
(names from 3.5 edition Player's Handbook p. 16)

Male Names: Aramil, Aust, Enialis, Heian, Himo, Ivellios, Laucian, Quarion, Soveliss, Thamior, Tharivol

Female Names: Anastrianna, Antinua, Drusilia, Felosial, Ielenia, Lia, Mialee, Qilathe, Silaqui, Vadanja, Valanthe, Xanaphia

Family Names: Amastacia, Amakiir, Galanodel, Holimion, Liadon, Meliamne, Naïlo, Siannodel, Ilphukiir, Xiloscient

Here we seem to have gemination at the end of words, vowel length, maybe uvular stop; th and ph are probably fricatives and not aspirated, judging by the presence of v and absence of f. Syllables seem to be (C)V(CC).

Using the very questionable methodology of taking the least common denominators of all of them would give us something like:

          Labial   Dental Alveolar Palatal Velar Glottal
Nasal        m       n                              
Stop       p b     t d                      k g
Fricative  f v     θ       s z                    h
Trill                        r
Approximant                  l       j       w

        Front Central Back
Close   i               u
Mid     e               o
Open          a

If you want an elvish language to be easily recognizable as elvish, you might be able to copy some of these features. I'm not sure, though, that there is any feature that might be universally understood as elf-like.

Answer 2

In addition to the phonological and phonotactical aspects given by @b a, I want to add some more phonotactical and statistical features for an Elvish language

• Preference of front vowels /e, i/ over back vowels /o, u/
• Restriction of word-final sound, words tend to end in a vowel or in one of the consonants /t, d, θ, ð, n, s, r, l/
• The two-vowel sequences /ae/ and /ie/ occur frequently. Laura Wattenberg calls the combination ae "the defining fantasy vowel". It is very frequent in fantasy names, even more frequent than in Welsh.