1. Focus on perfecting the obligatory prayers or any obligation in general.
2. Focus on the Sunnah acts, sunnah prayers and reading the Quran.
3. Fasting, Prophet Muhammad (SAW) would fast during the 10 days of Dhul-Hijjah. The only day we can't fast is the 10th day. We should try and fast on the 9th day. Day of Arafah. Fasting the day of Arafah forgives the sins from the year before and the year after when one fasts on the day of Arafah.
4. Make a lot of dhikr, the phrases are so light and easy that you can be doing it a lot on those first 10 days.
5. Sharing goodness. Share goodness to those who you love and others.