It is my personal opinion that you should not try to make a Tulpa unless you can admit to yourself that the only reason you're making the Tulpa is because you want to make a Tulpa. Additionally, creating a tulpa should not be a means to an end. What happens when you've accomplished your goal? What happens with the Tulpa? "I don't really need you anymore, but, uh, stick around I guess." That doesn't really fly IMO. If you have already read some of the posts here, you understand that what you are proposing is a very advanced technique. In addition to actually, y'know, creating the tulpa, you will have to nail down techniques that some folks who have been whacking away at for years have not been able to accomplish.
Separate your goals. Improving your personality is ACTUALLY NOT HARD if you ACTUALLY WANT TO DO IT. I can even prescribe to you a method right here and now. This might be a bit familiar if you have read any tulpa-creation guides, but instead of externalizing a trait, you will internalize it.
1: Identify a character flaw that you would like to abolish.
2: Think of potential situations in which that flaw would be brought out. Imagine what a better you would do instead. Resolve yourself to do it that way.
3: Constantly remind yourself throughout the day. Send yourself texts every few hours via IFTTT. Write it in ink on your hand. Create a representative bracelet out of yarn and wear it around.
4: When a situation comes up that touches on the trait, bring the Better You's actions to mindfulness and then immediately perform it.
A lot of folks think that doing this for 21-days will create a new habit that will be tough to break. Plenty of people dispute that, but there is some truth to it. We are what we repeatedly do is the cornerstone to almost every self-help book that has been written. I guarantee you that after a month of practicing your new habit, you will not have to think about it anymore and your personality will effectively have changed.
Make your tulpa anyways. Making forcing into a habit is one of the first parts of the process, and you're already making a habit anyways ;)