There is no short cut for this. You can do so only by spending time with the guy and finding out. External appearances can be deceptive and you could get fooled into forming an opinion which could boomerang on you. It is thus better to take your time to look at some basic criteria and evaluate him on those. While there is no guarantee to anything in life, you can at least have the satisfaction of having attempted a fair assessment and not regret the decision that you ultimately take.
Let us look at certain tips to find out how you can discover the frog or the prince in your guy.
a) Personal hygiene is of utmost importance and you should not compromise on this quality. Good looks though important should not be considered over good personal hygiene.
b) How does he speak and what manners does he show? Is he using the right grammar and do you think you will be happy listening to him through out your life?
c) It is always better if you are able to find somebody with a similar cultural and religious background.
d) Family background should also play a very important role in your decision to opt for a particular guy. When you have a loving and caring family, the chances are that your guy would have got his due share of affection and he is also likely to extend them for you and your children.
e) Educational backgrounds must not be very disparate. A huge difference may lead to problems later on in your married life due to issues of ego and a superiority complex coming into play.
f) Is he reasonably well settled in a job to provide for you? Make sure you do not go for the absolute workaholic as he may prefer to accord a much higher importance to his career than to you.
g) How enthusiastic is he about having children and what are his impressions about a complete family?
h) Do give a thought to his circle of friends and extended family. Are they well adjusted and in tune with your own temperament. If this is not the case, you could have problems going ahead.
i) Check out his immediate surroundings and personal effects. Does he maintain his car, desk and space well enough or he is very casual. If he appears to be very casual, then you cannot expect help from him for household work.
What about any vices or bad habits? While everybody has them, does he engage in petty gossip or cheat on tax payments. Is he hot tempered and prefers to spend time with his friends every other night?
The parameters are just some that you can consider and take a call. You may make a fair evaluation based on your findings and if your rating is generally positive with a couple of negative ones, you should be able to lead a comfortable marriage life in the hope that over time, you can iron out the negative attributes. After all, nobody is perfect.