A5) On Motivation and Relationship Forming
If the time/place of first contact occurs in space, or on/near some planetary body that is not native/generic to either the HE or AE [see A2], and having required extensive travel to arrive there, the AE may/will have likewise traversed great distances prior to this contact. Such journeys over vast distances [see A5) SPECIAL NOTE] are not undertaken without due purpose or imperative. Given this, what is/are the fundamental motivation(s) for this endeavor? The following are the most plausible:
Survival: Home-world destroyed or resources depleted, war refugee(s), or possible 'warrior class' military campaign, colonization effort-- possible detrimental/conflicted relationship [see A4, A1, A2, ]. 
Exploration: Scientific expedition/survey, exo-ontological collection, curiosity -- possible beneficial relationship. 
Alternative/Advanced Reasons: 'Religious'/mystical/spiritual pilgrimage or quest, solitude/loneliness: to communicate the curious experience of being-- possible beneficial, possible problematic relationship.
A5) NOTES: The above stated AE motivations are based upon the likely motivations of the HE. All assessments are ultimately reciprocal. 
A fundamental factor in consideration of any AE motivation, is the number of AEs that may be present or apparent upon first contact. A single, or small group of AEs may indicate an expedition or mission of some sort, whereas a larger group or population of AEs may indicate much more urgent circumstances, in that such a large number would be present all at once, making the whole vulnerable. Alternatively, a single AE may be difficult to assess correctly in terms of motivation. Numbers often betray motivations. The obvious is not always obvious [see A3.2)]. 
A5) SPECIAL NOTE: The greatness of interstellar distances is generally viewed as an obstacle to 'common' space travel as presently envisioned. However, a thoroughly advanced technology and/or cosmogonic theory may have been developed [by the AE or HE] to enable the safe and reliable broaching of cosmic distances. Such cosmological structures as 'worm holes' or Einstein-Rosen 'bridges' may yet be discovered and/or 'created' that could permit interstellar [or possibly inter-galactic] travel. Knowledge of these structures, and their navigational methods, may be a possible benefit to the other. 
In such a case as this, wherein one member/species in a relationship has knowledge not possessed by the other, it is advised to proceed with caution. Access to the means of efficient cosmological transport may be a 'secret' or privileged right. There may be preceding 'laws' [or equivalent regulatory agreements] and/or ethical standards amongst those who also share this knowledge. It is a highly problematic issue when a given HE/AE relationship involves the possibility of access to more advanced knowledge. Further, possessing the means/knowledge of interstellar travel may open the door to various forms of exploitation and/or abuse of this knowledge. Conditions may in fact be placed upon the transfer/acquiring of any such knowledge [see A6) Legal Concerns]. 
Alternately, a given AE, or group of AEs, may have arrived at a distant location via a 'multi-generational' journey, wherein the original [space-time span limited] AEs/HEs depart from their home world with the acceptance/fore-knowledge that said originals may not be alive upon the completion of a given voyage. Several generations [perhaps hundreds] of off-spring may have been necessary to carry the journey to its completion and final destination, if, in fact, there is a 'final' destination. If positive contact has been established with an AE that is generations removed from those that initiated its journey, it is advisable to probe [with due care to customs and rituals] the nature of this multi-generational journey. In such a journey, many generations may have arisen and passed on. It is possible that a new culture may have emerged amongst the AEs in the intervening time-span. Such a culture may find itself at variance with the culture of the originators, and this may prove to be problematic. There may be a division/disagreement amongst the AEs. The HE may possibly be drawn into this disagreement [and its possible conflicts] unknowingly. 
The fundamental injunction in HE-AE relationship forming is: Seek to know the culture. From this knowledge, the way to proceed will become apparent.