If you fast the tenth and eleventh of Muharram with the intention of making up missed Ramadan fasting, that is permissible and will make up for two of the days that you owe.

Tahiyyatul Masjid (“greeting the mosque”) is Sunnah according to most of the scholars, some of the scholars stated that there was consensus on this point.

There is no regular Sunnah prayer before Jumu`ah. What is prescribed is to offer whatever voluntary prayers you want from the time you enter the mosque until the Imam ascends the pulpit.

At forbidden prayer times, you can offer these nafl prayers: 1- The two rak’ahs following tawaf, 2- Repeating a prayer in congregation, 3-The Sunnah following Dhuhr prayer if one is putting Dhuhr together with `Asr, 4- One who comes in on Friday when the imam is delivering the khutbah; he may pray two brief rak`ahs, 5- The funeral prayer may be offered during the lengthy times when prayer is not allowed.

In tarawih prayer, you can say the opening takbir standing and then sit, or you may say the opening takbir whilst sitting, then when you feel more energetic you can get up, and this is better and preferable.

Salat al-Raghaib is a bid`ah that has been introduced in Rajab. It is done on the night of the first Friday in Rajab, between Maghrib and `Isha, and is preceded by fasting on the first Thursday of Rajab.