195. If one arrived to shul late and did not start Sh'mona Esrei together with the tzibbur, one may not begin Sh'mona Esrei if he will be unable to complete it (until Elokai N'tzor) in time to say Kedusha with the Tzibbur (by Shachris or Mincha) or in time to answer Amein Ye'hei Sh'mei Rabbah by Kaddish following Sh'mona Esrei (by Maariv), even if this means he will miss Tefillah B'tzibbur. Shulchan Aruch with Mishna Brurah 109:1

196. However, if one will miss zman tefillah by waiting to hear Kedusha or Kaddish, one should not wait, and should rather daven Sh'mona Esrei and miss Kedusha or Kaddish. If to make zman tefillah one must choose between waiting for kedusha (and he will not complete his tefillah in time for Kaddish), or missing kedusha (by starting his tefillah before Kedusha) but answering to Kaddish, Kaddish takes precedence. Shulchan Aruch with Mishna Brurah 109:1

197. If one arrived in shul timely, but regularly davens slowly with kavannah, and will not complete Sh'mona Esrei in time for Kedusha, he may nevertheless begin Shmona Esrei with the tzibbur, because at the time he begins he has a chiyuv of Tefillah B'tzibbur, and he is considered an o'ness in regard to later missing Kedusha.

Shulchan Aruch with Mishna Brurah 109:1, see also Bi'ur Halacha

198. Such a person is also permitted to begin his Sh'mona Esrei early, while the Tzibbur is still in middle of Krias Sh'ma, if this will allow him to finish his Sh'mona Esrei in time to say Kedusha.

Shulchan Aruch with Mishna Brurah 109:1, see also Piskei Tshuvos 109:1 and 90:16

199. If one waited to begin his Sh'mona Esrei until after Kedusha he may not begin Sh'mona Esrei unless he estimates that he will complete Sh'mona Esrei in time to answer Amein to the Bracha of Shoimeah Tefillah of the chazzan, {and he must also wait to answer Amein to the bracha of Ho'kel Hakodosh before starting to daven}. Shulchan Aruch w/Mishna Brurah 109:1

200. If one is waiting to begin Sh'mona Esrei (until after Kedusha or Kaddish, as the case may be), he should pause davening at "Shira Chadasha", and not complete the bracha of Go'al Yisroel, as that will trigger an obligation to begin his Sh'mona Esrei (because one must be "soimech Geulah L'tefillah"). Shulchan Aruch w/Mishna Brurah 109:1,2

201. Anytime that the tzibbur is saying Modim during Chazoras Hashatz one must say Modim and bow with the tzibbur so that he does not appear to be denying the belief in Hashem to whom the tzibbur is bowing. Shulchan Aruch w/Mishna Brurah 109:1,2

202. If one is in middle of Sh'mona Esrei he should bow (but not say Modim) at the same time as the tzibbur (so long as one is in middle of a bracha, or in between brachos. However, if one is at the beginning or end of a bracha one should not even bow - except if one happens to be at a portion of tefillah where one bows anyway). Shulchan Aruch w/Mishna Brurah 109:1,2

203. One who was unable to begin Sh'mona Esrei with the tzibbur and will not be able to complete it in time for Kedusha, should daven Sh'mona Esrei word by word with the Shliach Tzibbur. Shulchan Aruch w/Mishna Brurah 109:1,2

204. When davening Sh'mona Esrei word by word at Mincha together with the Shliach Tzibbur on a Taanis, one does not say "Aneinu" with the chazzan, rather, one says it in the place where the individual normally would say it; in Shoimeah Tefillah.

Shulchan Aruch w/Mishna Brurah 109:1,2

205. If one is davening Sh'mona Esrei word by word with the Shliach Tzibbur, he should say Kedusha with the Chazan, not with the Tzibbur, and he should also say "L'dor V'dor Nagid" along with the chazzan, as well. Shulchan Aruch w/Mishna Brurah 109:2

206. If one is davening Sh'mona Esrei word by word with the Shliach Tzibbur, according to the Aruch Hashulchan one may say Birchas Kohanim together with the chazzan. Other poskim say that it is better to remain silent and listen to the chazzan.

Aruch Hashulchan 109:11 and see also Piskei Tshuvos 109:3