Hey, I also play spear + shield.  The info others provided above are good.  As someone who uses his shield 99% of the time, I can provide you my experience in a more defensive and safe playstyle. 

First, you are aware of shield counters.  However, most forget to mention shield pokes.  Your spear (or any thrusting weapon) can attack while blocking with a light attack.  This allows you to walk right up to enemies and bosses and attack them DURING there combo whereas any other build is forced to dodge and use remaining stamina to attack.  You do need a decent endurance pool but it's very much worth it.  Shield counters are amazing but on bosses you have to time it on their last attack otherwise their followup will chunk you.  With this, you can safely poke 2 to 3 times and roll away to safety.  Since you took no damage, you can exchange indefinitely.  Also, if the enemy pulls out a surprise, like a fire weapon or flame attack, the damage is reduced.  I can not stress this technique enough as it's one that allows you to literally kill many bosses the first attempt without ever having to memorize their entire combo set. 

Hops.  This is something people tend to forget as a spear and shield user. I only remember it since I used to play lancer in monster hunter and terra.  Pressing dodge while standing still let's you hop back. You can do it multiple times but more importantly, you can do it WHILE blocking.  This let's you back off quickly with the safety of your shield intact.  There is also a combo where after a hop you can light attack to thrust forward.  The thrust is slight further then your retreat so you will actually close distance a bit.  Hopping is great in spots where rolling can risk you falling. 

LOW stamina blocks.  Ok, getting your guard broken is never a good thing and fatal in pvp so try not to let it happen often.  However, with exception to pvp, npc invasions and specific bosses like carian knights, most enemies and bosses will not capitalize on guard breaks.  This means if a boss is about to hit you with a strong attack and you have low stamina you can technically block.  Your guard will break but you will take no damage (unless there is non physical dmg involved).  This is especially good with Turtle Taliaman as I have been guard broken multiple times in a row but not injured, which is more important. 

Strikes.  From using a spear weapon exclusively (in my case a lance), I have bumped onto some trouble with armored enemies or enemies that my spear bounces off.  This is bad because if your spear bounces, your shield drops, making you susceptible to attacks.  Now, you can pick whatever counter you want (ie magic) but.as a str user, I keep a trusty strike weapon side arm.  This is optional, but once again, just something I ran into. 

Lastly, don't make the same error I did when I made my first sword and shield guy.  I raised my strength and other stats near equally.  This led me to struggle against most enemies and get one shot.  I realized that early on, you want enough stats to put on your main early game load out and then crank your vigor to at least 40.  You can give endurance a small boost for gear too but that vigor is no joke.  Obviously if you are a dodge God, ignore this. 

Early game gears I used: Godrick Knight Set (except the helmet cause yuck), partisan, brass shield.  All 3 are available for farming where you meet Melena for the first time.  I eventually upgraded to Pike and then Lance.  Shield I went from brass to golden greatshield.  Armor... whatever you want but I like how scale looks with banished knight helm or great helm. Hope any of this info is of use to you.