The druid is in sort of the same boat as the Amazon, however this character is for what can be called either a casting melee, or shape shifter.  This is due to the druid’s skill tree, as one set of skills is blocked no matter what form you’re in (most elemental spells can’t be case while in altered form and altered form skills can’t be used while in normal form).  This generally puts most druids into one of two paths: a casting melee or shape shifter.

Either form is going to require manna to fire off the skills/spells, while strength is needed for heavy armor/ weapons.  Thus your character is going to be a little weak till he matures in levels.  The good thing is that he has a lot of support as he has a lot of summoning options.

Defense wise if your going down the casting route use your spells to thin out groups and weaken enemies. If your going the shape shifter your going to be a close combat melee character and you’ll need to equip your self as such. Use your healing skills as often as necessary.  Shape Shifters will need to keep vitality in the cross hairs as the second concern for skill points. You will need the hp gained from this.

For casters, fissure is the first good spell you get.  The grand daddy of them all is Hurricane followed by Armageddon.  The last two are what you’re shooting for, as these will hit enemies around you allowing you and your minions to attack (thus giving them three forms of punishment: you, your minions, and the spell).  This is the most effective way to battle with the druid on a casting level.  But keep your guard up, as powerful as these two spells are they require you to be dangerously close to your prey.

Shape shifters will be fairly dependent upon their skills to keep them alive (but then again who isn't).  Use both the bear and wolf's strengths to your advantage.  The bear boats great defense and damage but has a slow attack speed. The wolf increases attack rating and speed but leaves defense normal. Careful use of both forms and their skills will turn the tide of battle.  Here's a brief run through on the better ones.

Feral rage (wolf form) will increase damage, speed, and attack ratting while giving all attacks a life stealing bonus.

Maul (bear form) increases damage, and attack ratting while briefly stunning the person hit.

Rabies (wolf form): infects a person with a poison that will spread to others close by.

Hunger (both forms): weak attack but extremely high life/manna steal rate (over 100% life/manna steal at lvl 3). Life steal only happens with the hunger attack. 

Shockwave (bear form) weak damage but stuns enemies for a second or two.

Casters: Use your minions to keep mobs off of you while hitting the mob with your spells. Be sure to keep your self able to handle a fight as you'll need to go melee from time to time (the druid will never be a pure caster).

Shape shifters: Don't limit your self to the wolf or bear.  The wolf can use feral rage or hunger to stem the tide of damage while rabies will sap life points from individuals in the group.  The Bear can use maul to quickly increase his damage and stun groups with shockwave.

Both types should keep minions near by to take some of the heat while you dispatch with the mob one by one.

Casters: Hit the boss while he/she is occupied with your minions. You'll have to go toe to toe with the first two bosses but you can attack from afar with the others.

Shape Shifters: Going this route will be harder than the casting one.  Be sure to outfit your self like a normal melee character and make sure that you have good resistances (very important).  Use a minion to distract the boss and hit him while he's occupied.  Avoid their more powerful magic attacks and use rage/hunger to slow your hp drain.  Be sure to leave a ranged attack item or equip a item that will give you a spell if things get to hard.  Generally, if you go solo don't expect to be able to take on bosses at the same levels as other character classes.  Magic attacks are your biggest concern.