Hej!	This is the most common way of greeting someone, be it in a formal or informal situation, and can be used as an equivalent of ‘How do you do’ as well as ‘Hi (there)’.
Tjéna[re]!	Informal and friendly. Actually an abbreviation of 17th and 18th century phrases like ‘Jag förbliver Eder ödmjukaste tjänare’ (I remain your most humble servant).
Tja!	Very informal and cool. An abbreviated form of ‘tjenare’, often in combination with ‘ba’ (tjá'ba), a reduced form of ‘bara’ (only), which in Swedish can be used like the English ‘sort/kind of’ as a filler without a real meaning.
God mórgon!  Good morning!	Used in both formal and informal situations.
God dag!  Good day!	This equivalent to ‘How do you do’ is mostly used to people you call ‘Ni’, e.g. elderly people, and on formal occasions.
God kväll!  Good evening!	The Swedish ‘good evening’ salute is nowadays mainly reserved for somewhat formal meetings or to people you address with the ‘Ni’ pronoun. The synonymous expression ‘God afton’ is rather antiquated by now.

Notes 

‘Tj’ is pronounced a bit sharper than the English ‘sh’ sound - as in ‘shut’, but with the middle part of the tongue pressed more towards the palate further back in the mouth (cp. German ‘ch’ in ‘ich’). 

Like in English some consonants change sound when they are followed by certain vowels (café - city; guest - gist). These so-called soft vowels in Swedish are: e, i y, ä, ö. The ‘g’ in ‘angenämt’, which preceeds the soft vowel ‘e’, is therefore pronounced like ‘y’ in ‘yes’, not like ‘g’ in ‘good’. Read more about the rules for pronounciation in chapter 9! 

If you just have been introduced to someone you might add: 
 

Trévligt att rå´kas/trä´ffas!  Nice to meet [you]!	Demonstrating that you are a polite and well-behaved person.
Ángenä´mt!  Pleasant/nice [to meet you]!	This equivalent to German ‘Angenehm’ and French ‘Enchanté’ is definitely old-fashioned, but could be popular among mature ladies.

Tack, [bára] bra!  Thanks, [just/only] fine!	Very common. Can be used no matter how you feel ...
Skapligt/Hyfsat  Fairly well/Decent	With the Swedish avoidance of superlatives. Quite frequent.
Så där/Det kunde vara bättre.  So there/It could be better.	Two variants of the same theme: "Not very well, but I'll survive".
Inte så bra, tyvärr.  Not so good, unfortunately.	(You are expected to show genuine concern when somebody tells you this.)

After having answered, you can return the initiative by asking him/her: "Och du/[du] själv?" ["And you/(you your-) self"]. After his/her reply, the greeting procedure would probably be considered finished.

Copyright Urban Sikeborg,
Stockholm 1997-1998.