you can start by LESS TALKING MORE RAIDING!!
but more detailed notes: (note: this is assuming you want to rule the lands yourself and not under a faction)
1. Start by serving as a mercenary for factions during wartimes, it helps with relations and can net you good troops/cash by helping in bigger fights.
2. Swear vassalage to a faction whom you have good relations with a number of lords. It doesn't have to be a lot (or any really) but it makes it easier to have a few friends around. As time goes you'll make more friends and other lords will start to respect you.
3. Obtain a fief. You'll probably get offered a village at first but, you eventually want a castle or a town. This takes good relations with both the king of the faction and his subjects. It's essentially a popularity contest BUT a lot of weight is given to the marshall or leader of the siege. (you don't have to be the marshall to lead one it just makes it easier to get more lords following you)
4. Once you obtain a castle/town you should start to train up troops. As many as you can afford and still post a profit weekly so you don't run into debt; not the end of the world but it does suck. Continue to partake in the wars of your faction, gaining fame and fortune, and more fiefs. Use this time to bolster your war chest and war capabilities, you want to get to a point where even if you lose a big battle you still have plenty of troops and cash that you can recover quickly.
5. This is the hard part; at some point you will feel ready to begin your own kingdom. What you need to do is conquer a castle or town by leading a siege yourself, but the king attempts to award it to another vassal. (tip: if he offers it to you, decline it and when he awards it to another you still get the option to rebel). You will get asked to accept his decision or claim it as your own and start your own kingdom. Doing so takes that fief and any others you own and turns them into your very own faction. But do beware, this will put you at war with the faction you just left.
6. Assuming you can hold your fief in time for peace; begin to make your rounds talking to other lords that are your friends. Get a feel for their status in their faction. You will have the option to try and persuade them to join you. This depends on a few factors: relations with you, relations with their king, what you offer them (lands, friendship, booty

)
7. As you amass other lords it would serve you well to keep your friends close by rewarding them with fiefs. Even ones you already own since it will improve their armies over time and keep them happy. Bigger fiefs to better friends, lowly villages to guys you don't care for but want to stick around. (tip: you can give friends villages to start if that's all you have, but at some point you want to reward your closest friends with the best fiefs.)
From their it's simply a game of ebb and flow, war and peace, politics and persuasion. Conquer lands, award to vassals and keep pushing.
You'll see that awarding some lords will annoy others, and some lords just have personalities that don't fit. It will take a while to conquer the world and while war can be fun you have to be careful about who you pick fights with and when. Being known as an honorable king will be useful down the road when brokering peace or persuading lords.
Hope that helps