Most adverbs are formed by adding -t to the stem of the adjective: vacker-t (beautifully), försiktig-t (carefully).

Few exceptions:

Adjectives ending in -ddhögljudd (loud)högljutt (loudly)
Adjectives ending in -enregelbunden (regular)regelbundet (regularly)
Adjectives ending in consonant + -dhård (harsh/hard)hårt (harshly)
Adjectives ending in -nnnoggrann (careful)noggrant (carefully)
Adjectives ending in -nnverklig (real)verkligen (really)

*A few adjectives form their adverb counterparts with a -tvis ending:
lycklig (lucky) - lyckligtvis (luckily)
möjlig (possible) - möjligtvis (possibly)
vanlig (usual) - vanligtvis (usually)
naturlig (natural) - naturligtvis (naturally)
Notice that some adverbs can be formed in both ways.

Time Adverbs

Some of the most common time adverbs:

aldrig - never
- then
förr - before
ibland - sometimes
nu - now
redan - already
snart - soon
sällan - seldom
alltid - always
genast - immediately
ofta - often
ännu - not yet
fortfarande - still

Location and Direction

Swedish differentiates between direction and location adverbs. The adverbs in motion are used with motion verbs such as ‘to go’, ‘to walk’, ‘to ride’, etc., whereas the adverbs at rest are used with ‘to be’, ‘to stay’, etc.

At Rest

borta - away
där - there
framme - forward, up here
hemma - at home
här - here
inne - inside
nere - down
uppe - up
ute - out
var - where

In Motion

bort - away
dit - there, thither
fram - forward, up
hem - home
hit - here, hither
in - in(to)
ner - down
upp - up
ut - out
vart - where, whither