With Investment trusts
Check Performance over 3 months to 10 years if it is available - particularly check relative performance against similar trusts i.e trusts in the same sector. I like Trust that usually out perform their rivals more than are out performed. In football look at Warnock's record is it better than other managers, he will have ups and downs but you get a sense of beating the average over time. Trusts can be similar
Check discounts/premiums - I don't buy trusts on premiums (underlying assets are worth less than the Trusts share price. Is the discount lower than average for the same trust over the last 12 months. An exception is venture capital trusts. Sometimes a discount can increase for no special reason there could be a buying opportunity.
What is the media saying e.g are there recommendations for the Trust from financial journalist(s).
I try and buy when something is not popular but has the potential to do much better. An example related to football would be Sunderland or Bolton or Charlton @ present. Unpopular sectors are Property, UK value companies, Japan (although changing), Emerging Markets. Alternatively sectors than look ordinary but could be big growth areas example at present Vietnam Trusts which are in the Frontier Markets sector. This style does not suit most people because they can't deal with it psychologically i.e buying when others are all selling. Most Professional manager would never do it, because if tehy do and they struggle they will be sacked. If you struggle and you did the same as everyone else you often keep your job. This can produce herding with professional managers. In the last 8 months they have all being buying big Tech until virus announcement.
Sometimes a new management team can make quite a positive difference.
After that fingers crossed.