Increase when you're confident.
The thing I used to do is, if I was doing something like 6 reps on a set, I'd get up to 9, then increase, because certainly on exercises where you were using both Arms or Legs at once in tandem, I knew putting the same small amount on, could get me back to 6 reps again.
If I was doing something involving dumbbells and alternating the working Arm or Leg, then maybe go up to about 11-12 reps approximately, as I would have to be mindful, that increasing weight with something like a Machine, Bar or two handed Cable, distributes the weight 50/ 50, onto or via both working Limbs / areas, but the same weight increase per dumbbell is then effectively using double the weight and that's not good.
To simplify. If you add something like 2lbs onto an E-Z Bar, you're splitting the 2lbs evenly with both Arms. If you do that increase with Dumbbells you get 2lbs per arm, not 1lb, like you would with a Bar.
So in most cases if it's an exercise with a tandem movement of two limbs, then 3-4 reps can be the amount you go up by, before adding a little more weight, but if you do alternating limbs, best to go up on a starting rep range, by 5-6 reps each time, before increasing.
As for a routine for you, I'd suggest incorporating certain movements.
Squats
Lunges
Deadlifts
Chest Press
Bent Over BB Rows
Skullcrushers
E-Z Bar Curls.
Planks
You only need to do the exercises with 8-10 reps, but if you're new to this, then try a simple formula, to help you adjust.
Small muscles like Biceps, Triceps and Delts, go for the lightest Dumbbells / Bar.
For bigger ones, go double that to start with.
Big muscles, smallest possible increase each week.
With small muscles, increase every two weeks, again as small as possible, as if you do it every week like big ones, you'll hit a rep max very quickly, especially on something like Delts, so you'll be doing potentially too much on small muscles, within 3-4 weeks.
Once you've been lifting for 6 weeks, to get used to it, then you could maybe go for a little more intensity.
Initially, go for 2 sets of 8-10 reps per muscle, except Planks, where you do 2 sets of 30 seconds, but each week add 5 seconds on. Giving yourself 15 seconds rest between both.
In 6 weeks, you'll be up to doing 2 x 1 minute on planks, touchwood.
For small muscles have a 1 minute rest period, for bigger ones, 90 seconds.
When you hit the 6 week period, and you're going close to rep maxes on all muscles, go for 3 sets of each, but for Planks, keep it at 2 x 1 minute, with 15 seconds between.
After a week of getting used to 3 sets on exercises, then you can start to make small increases again on what you lift.
Hopefully that all makes sense
