Be kind and forgiving of yourself. Change is hard work! It is always easier to keep on doing what you usually do (even when it isn't working for you). It is always harder to try to introduce change (even when change are good for you). The extra work and attention that self-help efforts require can be costly in terms of energy and emotional "growing" pain. People who are trying to change themselves for the better may end up becoming more vulnerable emotionally, and they may be at high risk for discouragement. They may tire easily, and they may find it difficult to stick with new changes and assignments, and feel very tempted to just quit. Part of making self-help work then is being willing to tolerate the pain of making the changes, and dedicated enough to hold onto the gains you make. You can also help yourself by not sabotaging yourself by doing things that will make it easier for you to fail.
Keep working your plan - even if you relapse or backtrack. Some amount of failure is inevitable. You're going to chicken out sometimes. You'll fail to meet some goals you've set for yourself. You're going to backslide. Don't obsess about such failures. Don't shame yourself or give yourself a guilt-trip. Instead, just dust yourself off and try again. At the end of the day, a little failure doesn't matter. Two steps forward and one step back is still one step forward. When it comes to self-help efforts, that one step forward can make a big difference in the quality of your life. Whenever you fail at working your plan, forgive yourself as best you are able and try again.
One common way of sabotaging your forward progress is to allow yourself to slip backwards into means of coping that are harmful to you. If you are an addict or person who has difficulties with substance abuse, for example, your big danger is that you'll reach for a bottle, joint, pipe, pill or needle when you feel stressed. If you are trying to lose weight, your big danger is that you will binge on food when you feel stressed. You cannot always avoid the tendency to backslide, but you can take precautions to help prevent temptation. If you are an addict, you can find sober housing and stop spending time with friends who will lure you back into using if given half a chance. If you are trying to lose weight, you can throw away all the cookies and other high-calorie snacks. In all cases, you can choose to spend time with people who will support your change efforts rather than those who would break them down. Stay away from toxic relationships - relationships which are abusive in nature, generally hostile, shame-inducing or which will result in substance use. Seek out positive, supportive relationships which will enhance your chances of success.
Do what you can do to stay with your change efforts - to not give up on them - even when you get frustrated (and you will get frustrated!) You set out to change yourself for good reasons, we assume. You are suffering in some way. Your problems are unlikely to get better all by themselves. If you don't help yourself, then things aren't going to get better.
If you really get stuck, reconsider whether self-help is the best way to go, and consult with a professional if the answer is "perhaps not". Working with a professional might be considered "Plan B" (the plan to use when you're sure that "Plan A" (e.g., self-help) isn't enough by itself). A qualified professional helper can provide you with motivation and guidance that can make the difference between your progress or lack thereof.