I have a question about the order of surahs to recite during first rakah, and second, and following.
I used to recite Surat ul Ikhlas after Surah al-Fatiha in first rakah. Will my pray be valid in this order?
What you've done is correct. Just to guide you, here is how the Prophet() himself taught somebody to pray correctly (with a long comment):
A man entered the mosque and started praying while Allah's Messenger (ﷺ) was sitting somewhere in the mosque. Then (after finishing the prayer) the man came to the Prophet (ﷺ) and greeted him. The Prophet (ﷺ) said to him, "Go back and pray, for you have not prayed. The man went back, and having prayed, he came and greeted the Prophet. The Prophet (ﷺ) after returning his greetings said, "Go back and pray, for you did not pray." On the third time the man said, "(O Allah's Messenger (ﷺ)!) teach me (how to pray)." The Prophet said,
"When you get up for the prayer, perform the ablution properly and then face the Qibla and say Takbir (Allahu Akbar), and then recite of what you know of the Qur'an,
Note that scholars say one must recite the fatihah (surat al-fatiha) before reciting some other surah based on this sahih hadith, else if a person can't recite al-fatihah one may recite: "SubhanAllah, wal-hamdulilah, wa la illaha ill-Allah, wa Allahu Akbar, wa la hawla wa la quwwata illa Billahil-aliy al-azim (Glory be to Allah, praise be to Allah, there is none worthy of worship except Allah, Allah is Most Great, and there is no power and no strength except with Allah the Exalted and Magnificent)" based on the hadith narrated by an-Nasa'i and abu Dawod here and here), but one should learn to recite al-fatihah as the recitation of al-fatihah is necessary (mandatory) according to the view of most madhabs based on ahadith such as the one quoted above and in Muwatta' Malik and Sahih Muslim and therefore one should put effort in learning it to make the prayer more complete.
and then bow, and remain in this state till you feel at rest in bowing, and then raise your head and stand straight; and then prostrate till you feel at rest in prostration, and then sit up till you feel at rest while sitting; and then prostrate again till you feel at rest in prostration; and then get up and stand straight, and do all this in all your prayers." (source Sahih al-Bukhari)
Also note that "what you know of the Qur'an" may refer to anything like surat al-Ikhlas or a few verses such as ayat al-Kursi or anything else you have memorized of the qur'an. You even may repeat al-fatihah or repeat the same sura in the second raka'a!
Also take a look at these relevant posts:
Going from "never prayed in my life" to my first prayer??
Can we recite two or more surahs in one rakat when praying?
The order of Surahs in Prayer?
So i use to recite surat ul ikhlas after surah e fatiha in first rakah. So will my pray be valid in this order?
Yes, of course your Salah (prayer) is true, even though it is said that reciting Surah Ikhlas (Tawhid) after Surah-Hamd has priority, albeit it is not wajib (obligatory) to definitely recite it. Hence your Salah is true in that situation.