The Hebrew word for trustworthy is ameen. It comes from the root meaning faithful. When we consider what it means to be trustworthy, it is really a component of faithfulness. And one of the best examples of trustworthiness is Hashem Himself.
We read of this in Exodus, when Moshe declares the 13 middot of Hashem:
"Merciful God, merciful God, powerful God, compassionate and gracious, slow to anger, and abundant in kindness and truth. Preserver of kindness for thousands of generations, forgiver of iniquity, willful sin and error, and Who cleanses." — Exodus 34:6-7
Hashem is so trustworthy. As it says above, He is the "Preserver of kindess for thousands of generations..." He is faithful to forgive us, He doesn't stop in His mercy. And He keeps going on and on with this. As we have seen from Psalm 136, "His kindness endures forever". He can be trusted to be there and to always abound in kindness. This kind of trustworthiness is emblematic and a beautiful example for us. If we aspire to increase our trustworthiness and be a sign to those around us, then our focus should be to become more like our Creator (albeit in our own, small way).
(For more information on meditative techniques, see the source Jewish Meditation by Aryeh Kaplan.)
Find a comfortable seat in a safe, quiet place. Breathing in slowly, allow your stomach to completely inflate which in turn helps your lungs to competely inflate. As you exhale, gently pull your stomach in, squeezing all the air out of your lungs. Deep breathing brings oxygen to your brain and helps clear the mind. Continue breathing until you feel relaxed and feel little or no distractions. Let the noises around you, no matter how small, filter out. Focus on your breath.
The focus of this meditation will be upon the psalm verse below. Choose whether you will say the Hebrew or the English. Both are provided below:
:נֹצֵר חֶסֶד לָאֲלָפִים
(Notzer Chesed l’Alaphim)
Preserver of kindness for two thousand generations...
--One of the 13 Middot of Hashem, Exodus 34:7
Meditate on this phrase for at least 10 minutes without interruption. Consider how Hashem has been trustworthy to past generations. Consider how He has been trustworthy and faithful in your life. As you continue to meditate, breathe in slowly, and when breathe out say the phrase above gently. As you speak this phrase on your exhale, continue to reach a deeper level in its meaning, dwelling on how you can better emulate your Maker and help others put greater trust in you. Contemplate on whatever is your weak point that might cause others not to put their faith in you (lateness, saying things but never coming through, broken promises, sporadic behavior, failing to answer correspondences, etc...).
As you slowly and gently end your meditation by opening your eyes, try to maintain a sense of quietness for a time after—allow the experience to flow through you and feel its effect.
The goal is to help you become aware of how trustworthy you are. If you properly focus during meditation and allow yourself to dig deeply into your life and root out your inconsistencies, over time you will achieve a higher level of trustworthiness. By becoming more faithful in matters, simple to great, people will put greater trust in you and your relationships will flourish and grow. Through all of this, you will be a better witness of the Divine in your words and deeds.