A Personal Trainer can be an effective addition to your goals, however only if they know what they are doing. But just helping you stick to your gym appts and being motivated is great!
Just asking questions will be your first clue. If they don’t like answering them and just want you to do as you are told, get someone else.
Ask what type of routine and exercises you’ll be doing. If it consists of high reps on machines - get someone else. It may be good to start with high reps and machines depending on your current level, but you should be heading to free weights and lower reps asap.
Variations of the squat, deadlift, row, pullup, and presses should be staples. If they want you to do lots of tricep kickbacks while standing on a medicine ball - get someone else.
There shouldn’t be lots of talking and resting going on in your workout, otherwise it’s a waste of your time and money. You should be constantly moving.
Check what type of micro-cycle/meso-cycles you will be doing. They shouldn’t leave out any muscle groups, and preferable concentrate on movements instead of muscles as in the above exercises. If they want to start you off on a bodypart split (chest, arms, legs, etc) probably not a good idea - ask if that will ever change. A lot of trainers are supposed to follow certain guidlines - they may change the exercises but not the reps and muscles trained - get someone else.
Check their nutrition knowledge. If they push supplements - be very wary. The basics that should never change are the 7 habits by Dr. JB. If their nutrition paln varies widely from this - be wary.
Here’s the link to the 7 Habits:
Also - I can’t stress how important it is to be wary of the sales side as well. They may try and rope you into a yearly contract or pay overly high prices. You shouldn’t start with anything more than a 3 month or 36 session contract - what if you don’t like the trainer? And a good starting point for session pay is around $40-70 per hourly session. It’s possible to get good trainers on less and excellent trainers on more - but really make sure. Make sure you are getting your money’s worth and aren’t stuck with something you don’t want.
Congrats on getting in gear to achieve your physique goals. Be diligent and you’ll do well.