Yesterday, some guild members were explaining in guild chat about their bad experiences in PvP (long losing streak, inexperienced teammates). I have some suggestions which may help.
If you are doing the Year of the Ascension League achievements, load three of your characters into the Heart of the Mists at the start of your PvP session. Each of the four parts of the Year of the Ascension requires the player to win a specific number of matches with different professions. Before the match begins look at your team's composition and the opposing team's composition. If you are playing a guardian and your team has two other guardians, consider switching to another class especially if the other team has three or four condition damage professions. If you are playing a longbow ranger, and the opposing team has three thieves definitely switch professions. Be flexible and try to improve your odds of winning the match.
When I play during the league season, I set a limit of three consecutive losses which if reached means I do something else either in the game or log off. You can set your own limit just don't continue playing when you are not enjoying the game. A losing streak could mean that ArenaNet's matchmaking system is working against you. Look at this post in the GW2 forum:
https://forum-en.guildwars2.com/forum/game/pvp/Matchmaking-seems-kinda-odd-eh
The attachment provided by the original poster shows that he, a Legendary ranked player, was teamed up with three other Legendary rank players and one Diamond player versus a team of five Diamond players. According to the poster, all players were solo players and this occurred in the three matches he played.
Chaith of the Astral Authority pro league team recommended playing only during the NA prime time when the pvp population is higher to increase your chances of getting better teammates. I've done that this season and have had winning streaks of five and four games as a solo player.
Good luck to everyone this season.