Warning: this is a bit long.
I've been RPing long enough that it isn't an issue for me to separate characters from myself, they are two completely different personalities and persons that do two completely different things. The first step is consciously reminding yourself that the character is someone else who's goals and hopes may be completely different than what you, as the player, want. It is often helpful to create a character who disagrees with you on something major so that you can practice making a real and genuine character who believes in a goal that you, as the player, may wholeheartedly disagree with. This may be too much for a lot of beginners, so an easier way to learn is to have your character get embarrassed or otherwise humiliated in some way so that you can practice having the character be upset while you the player are not. Enlisting another player to play a practical joke on your character is an excellent way of doing this because it does no actual harm and it is the type of thing where absolutely any character could have walked into it (yours was just "at the wrong place at the wrong time", from their perspective) but still presents a circumstance to get humiliated in some small but utterly depreciating way. (It also lets other people join in the fun, but that is an entirely secondary benefit.) Remember that not all characters get upset in the same way; some get huffy, some go into a rage, some withdraw, some get frazzled, some try to get even, and some act like they laugh the thing off but hold a grudge. And there are a million other ways that a character can react to something like that, the important part for this exercise is for the character to react in some way that is both different and less good/less acceptable/etc than you, as the player, either would or would want to act.
The second step is to recognize the difference between IC and OOC motivations that have an effect on the character. This requires recognizing that OOC motivations do, in fact, have an effect on the character even though their IC motivations are completely different. Neither of these are "bad", so long as they are used well, but learning to use them well and even learning what "using them well" means can be a major hurtle in and of itself. Let me give an example to illustrate. Lets say that you have the OOC motivation to have what you think of as an "AWESOME" character. That is a fine motivation, despite the simplicity of it. But if your character's IC motivation is the same, to be viewed as awesome, than they would be a horrible show-off, would take stupid risks, and would have to have something about them that would give them an advantage over everyone else despite the fact that all characters are created with the same basic rules. When all is said and done, a character with that motivation would not be very "awesome" at all, from a player's perspective, even if they might be fun for other reasons. But this can be accomplished much more easily if the character has another motivation; such as upholding justice, overcoming adversity, or defeating the race of "monsters" who killed your character's little sister, etc. Each of these IC motivations can easily lead to having an "awesome" character, but it also leads to the character being more "real" and "genuine" by adding in weaknesses and faults as well. What motivates the "justice" seeking character to be such a zelot for a cause that most other characters acknowledge and want but are less determined to follow after? What happens when the character who wants to overcome adversity runs into something that they cannot overcome, such as having had a prank pulled on them and having walked into it? What type of rage or other dirty motivations drive the character to wipe out an entire race? Every character has weakness and falters on seeking after their goals, both the IC and OOC ones, but that only makes their eventual victory ever more sweat.
But then the question is begged. Why talk about OOC motivations as being important to the character when the character itself is supposed to act according to IC motivations and not OOC ones? The simplest answer: because you the player need to have fun playing according to what motivates you or else nothing will happen to push forward the IC motivations because you will simply stop playing. Is that a simple and direct enough answer? How about a more complicated one then: Because OOC motivations will have an effect on the character, by virtue of the very fact that the character is being controlled by an OOC person and all things other than IC experiences come from that OOC source; therefore you need to learn to use these motivations constructively rather than attempt to deny the existence of them. Let me remind you, if the character does something simply because you the player wants it to happen and not because they the character have some reason to do it, then you are doing something wrong. But also consider how far OOC motivated things actually do go. Almost every bit of every philosophy or religion or morality, including the specifics of practice, comes from OOC ideas; all we have IC is the very basic things in the books/on the main page and from the characters experiences with other characters who take their ideas from the exact same places our characters do, so it all comes back to something that someone made up OOC or from the very limited and broadly defined things that the GMs have given us. Every bit of the character's back-stories before they came to Gobaith happened for OOC reasons, since none of our characters were actually played in Salkimir or wherever. Excepting the few things that had happened since the character arrived in Gobaith, everything about a character's personality and motivations and morality were chosen for OOC reasons. On a larger scale, since all actions on Gobaith were taken by characters (whose choices were ultimately designed by the OOC decision to make their IC motivations to be of one type rather than another), there is not any action that has been taken by any character in the entire history of Gobaith that does not have some OOC influence attached to it. I could go on, but I believe my point has been made: OOC is important to what happens IC.
While there are quite a few "competent" RPers whom I define as people who understand the point that "the character is not you", I find very few players or writers in general who have progressed to the point of being "good" by virtue of understanding both the effects and limits of OOC motivations on the character.