Negative self-talk specifically is related to the automatic negative thoughts that we might have about ourselves or the immediate response in our head after something has happened to us. It's the "Oh no, s/he thinks I'm an idiot. I'm starting to feel sick about this." Or even further and in the deepest part of our mind "I'm worthless and no one cares about me." This can originate from something we might have heard from others or past experiences. It also tends to be repeated often.
I found a brilliant quote the other day about self-talk - "You've been criticizing yourself for years and it hasn't work. Try approving yourself and see what happens." - Louise Hay. This is exactly what needs to happen. Give yourself a break and credit for the good things that you do! Start turning these negatives into positives and help build up things such as self confidence and self-esteem.
One challenge that you can do it look at yourself in the mirror. Practice repeated statements over and over again such as the ones below. If you can, give a different example each time that you try it.
1. I am a strong person. I was strong when ...
2. I am capable of being happy. A time when I was truly happy was ...
3. I am a good (friend, mother, sibling, spouse, etc.) A time when I was this was ...
4. I am capable of making decisions myself. A time I made a good decision was ...
5. I am lovable. People who love me without hurting me are ...
6. I am talented. One thing I am good at is ...
7. I have strengths. One of my many strength is ...
There are several positive statements that might fit yourself, so speak to what fits your current negative self-talk. The most important part is saying it out loud. Not just in our head. Saying it out loud will help you start to believe it by putting it out there. Watching yourself is also important to gauge your own response and see the smile that it hopefully brings out in you and a positive change that you can make for yourself.
Be nice to yourself, you're the only you there is and often times we're our worst critics.