1. Mantra- "Ek Ong Kar Sat Gur Prasad is known for its powers to reverse negative into positive, Negative circumstances, Negative habits, Negative minds, negative surroundings.. and this Mantra has power to convert them all to positive. There is one Creator of all Creation. All is a blessing of the One Creator." (from meditativemind.org).
You can meditate with this mantra, chant it a few times when you feel like you need to clear some negative energy or play it in the background in your car or your home. Here is a beautiful version.
2. Segmented Breathing: 4 parts in, 1 part out for healing, energizing, uplifting. Inhale through the nose 4 equal segments or sips of breath, filling the lungs completely then exhale one smooth breath out of the nose. 3 minutes is great for a quick boost or mood shift.
3. Shower or wash hands and splash water on your face. Even a really quick rinse in the shower helps discharge negative energy and lift the mood or bring you back to neutrality. I learned this tip years ago and I am still amazed at how well it works.