There is an accepted custom to answer “baruch hu u’varuch shemo” (BHUS) to someone’s beracha after the shem haShem is said (unless one is being yotzei with that beracha). During chazaras hashatz one must be careful not to allow that to have him or her miss answering amein. Also, BHUS should not be drawn out, and the chazzan should wait till the BHUS of the tzibbur is finished, as the tzibbur must hear every word of chazaras hashatz, especially the concluding words of the beracha.
If one “lost their place” during shemoneh esrei:
- If somewhere in first 3 berachos, he should start shemoneh esrei again.
- If somewhere in the last 3 berachos, he should go back to “retzei”.
- If during the middle berachos, he should start again from the first berachah that he is unsure that he said.
Even if someone feels that they will have more kavana if they daven alone, davening with a minyan is preferable. (Igros Moshe OC III:7)