This is the correct procedure for the worship of Sandhya in the morning given by samavartaka

पादौ हस्तौ प्रक्षाळ्य द्विराचम्य दर्भपाणिः प्राणानायम्य प्रातस्सन्ध्यामुपासिष्य इति सन्कल्प्य वारिणा पुंट्रं धृत्वा आपोहिष्टेति मन्त्रस्य सिन्धुद्वीप ऋषिः गायत्री च्चन्दः आपो देवता इति शिरो मुखहृदयेषु विन्यस्य प्रोक्षणेविनियोग इति विनियोगं स्मृत्वा मन्त्रार्थस्मरणपूर्वकं आपोहिष्तेति तृऋचस्य आदितः सप्तभिः सप्तविप्रुषश्शिरस्युक्षिप्य अष्टमेनैकाम् विप्रुषं पादयोर्निक्षिप्य नवमेनैकां शिरस्युल्क्षिप्य सप्रणवव्यहृत्या आत्मानं परिषिञ्चेत् ततः सूर्यश्चेत्यनुवाकस्य अग्नि ऋषि गायत्रीछन्दः सूर्यो देवता आचमने विनियोग इति पूर्ववद्विन्यस्य विनियोगं च स्मृत्वा अर्थस्मरणपूर्वकं सूर्यश्चेत्यनेनाभिमन्त्रिताः आपः पीत्वा द्विराचमेत् दधिक्रव्ण्ण इति मन्त्रस्य वामदेवऋषिः अनुष्टुप् छन्दः विश्व्वेदेवा देवता दधिक्रावावा देवता मार्जने विनियोगः इति पूर्ववद्विन्यस्य एतया सुरभिमत्या आपोहिष्टादिभिस्त्रिस्त्रिभिश्च पादशः मार्जयितवा पूर्ववदात्मानं परिषिञ्चेत् ततः अर्घ्यप्रदानम् करिष्य इति सन्कल्प्य गायत्र्याश्च वक्ष्यमाणमृषादिकं विन्यस्य तदर्थम् च स्मृत्वा अभिमन्त्रितं जलाञ्जलिं सूर्यायार्घ्यं थ्रिरुत्क्षिपेत् तत आचम्य सजलेन पाणिना सकृदात्मप्रदक्षिनं कृत्व असावादित्यो ब्रह्मेत्यात्मानं ध्यत्व हृदयमभिमृश्याचम्य यथाचारं ग्रहादींस्तर्पयेत् इति संवर्तकः।

paadau hastau prakSaaLya dwiraachamya darbhapaaNiH praaNaanaayamya praatassandhyaamupaasiSya iti sankalpya vaariNaa puMTraM dhR^itwaa aapohiSTeti mantrasya sindhudwiipa R^iSiH gaayatrii chchandaH aapo devataa iti shiro mukhahR^idayeSu vinyasya prokSaNeviniyoga iti viniyogaM smR^itwaa mantraarthasmaraNapuurvakaM aapohiSteti tR^iR^ichasya aaditaH saptabhiH saptavipruSashshirasyukSipya aSTamenaikaam vipruSaM paadayornikSipya navamenaikaaM shirasyulkSipya sapraNavavyahR^ityaa aatmaanaM pariSi~nchet tataH suuryashchetyanuvaakasya agni R^iSi gaayatriichhandaH suuryo devataa aachamane viniyoga iti puurvavadvinyasya viniyogaM cha smR^itwaa arthasmaraNapuurvakaM suuryashchetyanenaabhimantritaaH aapaH piitwaa dwiraachamet dadhikravNNa iti mantrasya vaamadevaR^iSiH anuSTup chhandaH vishwvedeavaa devataa dadhikraavaavaa devataa maarjane viniyogaH iti puurvavadvinyasya etayaa surabhimatyaa aapohiSTaadibhistristribhishcha paadashaH maarjayitawaa puurvavadaatmaanaM pariSi~nchet tataH arghyapradaanam kariSya iti sankalpya gaayatryaashcha vakSyamaaNamR^iSaadikaM vinyasya tadartham cha smR^itwaa abhimantritaM jalaa~njaliM suuryaayaarghyaM trirutkSipet tata aachamya sajalena paaNinaa sakR^idaatmapradakSiNaM kR^itwa asaavaadityo brahmetyaatmaanaM dhyaatwa hR^idayamabhimR^ishyaachamya yathaachaaraM grahaadiiMstarpayet iti saMvartakaH.

After cleaning the hands and legs and doing aachamanam twice, wearing darbha, and after performing pranayaamam, we should do the sankalpa that i am going to perform the worship of the morning sandhya.. and with the manthra aapo vaa idagm sarvam, we should smear our forehead with water, the devata, rishi and chandas for aapohishta manthra are water, sindhudweepa and gayatri, and with the full understanding of the triple r^ik one should sprinkle water on the head seven times, legs on the eighth time and head on the ninth time with manthra aapohista mayo bhuavaH etc. for the manthra suuryashca maa ..the rishi is agni, chandas is gayatri and suurya is devata.. remembering them and knowing the meaning of this manthre, it should be applied for the special aachamanam suuryashcha maa manyushcha etc manthra and keeping water to the extent of summerging a green gram, and should drink the water after chanting the manthra. Then remembering the rishi chandas and devata of the mantra Dhadikravnno akarisham... vamadeva rishi, anushtup chandas, vieshwedeva and dahikraa are the gods for this mantra and it is used for cleaning oneself befor arghya.. the procedure of sprinkiling water same as aapohista.. yasya kshayaya.. alone to sprinkle the legs and others sprinkling the head.. After this the rishi chandas and devaat for Gayatri have to be remembered and meditating upon the meaning of Gayatri, one should fill the palm with water thrice and pour water on the ground thriece. Then after aachamanam, one should take water on the right hand and with sprinkling water should take the hand around oneself in clockwise direction and touching heart should remember, this supreme soul is aaditya, it is me and it is truth and brahma is truth and I am that brahman. Then again aachamanam. Praayaschittharghyam is not given here because originally there is no provision for delay. Then one should do the tarpanm for the planets etc according to their respective aacharaas. Smarthas and vaishnavaas do tarpanam forK esava etc, but shaivaites do that for Lord Shiva

At present we do not use dharbha for sandhya, and usually the rishis chandas devata etc for the manthras are not mentioned. The aachamana manthras will change for Maadhyaahnikam and Saayam Sandhya. The meanings of prokshana manthras and aachamana manthrs have to be taken up separately. The usual aachamanm with fingering rules have also to be dealt with separately.