Try to find out why you lost, every time you lose. Don't bury your mistakes or you're nearly guaranteed to repeat them.
Also, even more important: Cultivate your enjoyment of chess, and don't let issues like score and rating drag you down.
If you want a specifically chess tip: try to make all your pieces work together rather than falling in love with just one. When you don't know what to do, try to improve your worst piece.
Have fun. If you dont enjoy what you do, youre not going to be motivated to work hard.
Same advice I'd give anyone... at any level: Play a lot of chess. There really is no substitute... books and analysis are helpful, but nothing beats the experience gained from continual play! 
What is your best chess tip for a player rated 1248? It can be 1,3 or 5 lines of text or whatever you like.
Study and learn THE BRAIN FRY ATTACK, an wonderful attacking chess system:
Ask for chess analysis from this promising and very good start-up, THE KING OF PATZERS CHESS ANALYSIS, INC.:
Play chess to enjoy. If you like chess, play many games, improving comes naturally. (up to a certain level)
Play, play, play, eller sagt på en anden måde: Spil en masse partier, og analysér de partier, hvor du fik en andenplads 
Do a 'blundercheck', i.e. always examine your opponent's checks and captures before making any move. When you have gained proficiency, add studying your opponent's threats to the above checklist. Also following your own advice is good (I often fail to do a blundercheck, with disastrous consequences).
try to keep your pawns unified?
Review your games. Try to find improvements that you missed.
Read some quality chess books, if you have the time.
Don't hang your pieces. Don't hang your pieces. Don't hang your pieces.
Win games
At that level, the first concern should be to avoid hanging pieces. Don't make your move until you've figured out what your opponent's likely reply would be.
The second concern is to finish your development quickly. Unless there's a tactic, you should try to develop all your pieces before you move any of them a second time.
Third, learn the basic endgames. I recommend Silman's endgame course.
https://www.amazon.com/Silmans-Complete-Endgame-Course-Beginner/dp/1890085103
https://www.chess.com/forum/view/general/comprehensive-advice-for-improving-your-game
Best and most comprehensive advice that you'll ever find.
whether not wether
Your syntax appears to be incomplete, spawkle529.
no one cares im just trying to correct him
What is your best chess tip for a player rated 1248? It can be 1,3 or 5 lines of text or whatever you like.