Who should I give titles to?

I've been playing for a few days, but still I'm not sure who should I give or not give land titles. Should I give it all to my heir so when I die he gets everything? Or should I spread it to people in my family? or maybe to people not in my family? (I've noticed some vassals in my family (with the little blood drop) have like a -50 relationship penalty with me for wanting a duchy or something like that.

In that order, should I give even more titles to vassals that don't like me trying to appease them or is it just worsening the situation (like, will they start hating me again after a while, but now with a bigger army to fight me if they rebel)?

Great game, but so confusing.

There is no one-best-recipe.

Your vassals should never have too many titles - in this case they will have power to singlehandedly overthrow you and usurp your title or make you to lower crown authority or taxes or levy size. And be sure - there will be time when they want it.

Also don't give titles to someone who hates you - in this case make them your vassal's vassal - this is a suitable solution for unlanded sons or brothers. It also makes them harder to raise war for your crown, because they should firstly became duchies, and this involves war with their liege, whom they may hate no so strongly.

Give titles to ppl who have Content trait (+50 relations), to someone with same sins and virtues as you, also try to make your king as good as your can - virtuous, kind, just, prestigious, pious.

Look for vassals' background - don't give land title to priests and mayors - they will have "Wrong government type" penalty.

Respect - is everything. You can fight with rebel vasslas, but not with all of them at the same time.

Hope they will be helpful!

I generally give land to members of my dynasty. The more landed members in your dynasty and the higher their prestige the bigger the prestige bonus when you start a new king and the lower the probability that you'll lose(or that titles will pass out of your dynasty.
Generally my recipe is this:

1. Make sure all male members of dynasty have wives with high fertility. Alliances and titles are less important IMO than additional sons in the dynasty.
2. Make sure all female members of the dynasty are in matrilineal marriages. For members that aren't in your court recruit a courtier and then bribe your dynasty member to marry him.
3. Split the land you get evenly between male dynasty members and female members in matrilineal marriages. Even though they might not like you as much because they have indirect claims, they generally won't dislike you at the same time.
4. For vassals that are not dynasty members, induce them to rebel(levy their troops or make them court jester), or discover their plots with your spymaster. Then you can imprison them without penalty to other vassals. After they're in prison you can seize a title without penalty(Because they're a traitor), then give it to a dynasty member.

Other than that, try to make sure that your king's wife and you have high statesmanship so that you can manage a larger demense. And once you've got some decent troops you can seize a lot of land in holy wars without all the issues seizing claims etc. This is great land for buying off dynasty members that are threatening. Because of the debuff the land takes for a different religion conquer, your member won't be able to levy any troops on the land for 30 years. I once had a rebellion where the vassal could levy no troops at all.

Also ,I've found that you can win holy wars against some of those enemies with large coastlines even if you have fewer troops if you're tricky using ships. Basically, drop your troops in one end of their territory spread them out to the minimum needed to siege as many territories as possible. Hopefully you can win a couple sieges before the enemy 10k army makes it over your way. (You can place a couple ships further down the coast as scouts, or even use a council member.) Once the huge army makes it close, retreat to your ships. Don't fight it! Then use your ships to transport your army to other end of their coastline and start sieging over there. Rather than liberating the territories that you've already won, the enemy tends to walk all the way to where you started your new sieges. Since you used ships you can get there many months before them.

This is even easier if they're in another war, because their massed armies will tend to get distracted by the other enemy, giving you more time for conquering territory.

Do not give duchies to your relatives! This just sets you up for a nasty succession crisis.

You want to give one or two duchies to your successor so that they can start building up prestige. If you are going to do this when they are a child then make sure you betroth them first.

Give your other duchies always to unlanded courtiers from a "nobody" family. Try to pick courtiers with positive traits. Do not pick people that hate you although keep in mind that giving away a duchy will give you an opinion boost. Do not give land to anyone with the ambitious trait.

A rebellion here or there is fine. You can raise levies from your other dukes to crush them.

The more prestige you have, the more your vassals will like you. War is your friend! You get more prestige from fighting in wars that you did not start, so do honor those alliances as much as you can.