TROUBLE SHOOTING TIPS - Horse not going forward, hitting fences or breaking gait

Horse -  Not going forward
The horse responds to clear progressive training and instruction. If the rider is not focused and positive in the desired aim, the negative effect will culminate in uncertainty in the horse and lack of willingness to go forward into the unknown.
A passive rider or one restricting the forward motion by hanging on to the reins to tightly, will very quickly stop the horse's confidence transmits a feeling of anxiety.
Organise a structured progression through training with defined aims and timescales.
Rider and horse must progress at a comfortable level, which will encourage confidence to both and therefore enthusiasm.
 Rider - Feeling Frightened 
A previous bad experience or lack of training can result in fear and anxiety. Use positive thought and attend jumping clinics or instruction from a professional trainer to encourage your progression and build confidence. If your horse is very strong or becoming out of control, try and stop as soon as you can; you are a danger to yourself and others. Ask for advice on biting or flat work exercise's which may help you both relax and enjoy the experience rather that running in fear.  

horse refusing to jump
Horse - Hitting fences with the front legs. 
Stiffness in the hind legs can prevent them from being together and fully underneath the horse to create enough propulsion for the jump. If they are weak and therefore too far away from the fence the highest part of the fence will be knocked on the way up and the horse will jump flatly.
Taking the stride too close to the fence will also be a cause, as the horse will not be able to snatch up the front legs in order to clear the obstacle.
More flat work and use of jumping grids will be very helpful for learning the pace, stride length and collection.
Rider - Riders position ahead of the stride. 
If you are gripping with the lower leg too tightly the upper body goes forward to keep the balance. Over exaggerating the jump is a common fault, do not jump the fence for the horse, and allow them to jump beneath you keeping a centre of balance behind in the saddle rather that propelling your body weight onto their shoulders. Lighten you leg contact slightly, keep an even contact on the reins to support the horse and don't try too hard.
 breaking gait

Horse - Breaking gait in a trot and walk.
Insecurity in aids and lack of calmness in the horse can be a cause, go back to movements and transitions which you both find easy which will relax the situation. Lack of impulsion and inconsistent contact also allows the horse to take the easy option of breaking the gait.
Over riding and continual niggling with your heels can often result in the gait being broken as the tightening in the seat, tightens the horses natural pace.

Rider - Bumping in Sitting Trot 
Suppleness is the key here, good posture and control of the core and lower back are crucial: try some exercises off the horse to help. Stiffness in the horses back makes the rider bump more which in turn stiffens the horse more, concentrate on your seating position in walk and canter using lots of transitions and stay relaxed. Sometimes your saddle or length of your stirrups can help, try a different saddle and find your most comfortable natural sitting position for your horses stride.

Read more riding articles and tips here 
Horse - Refusing or stopping.
Are you unbalanced and insecure in the saddle when jumping?