Particularly, payroll taxes, which in some countries (France) are at 50%. These hugely complicate hiring employees, and just encourage cash payments and tax avoidance. Taxes should instead be shifted to harmful outputs and products, like food sweeteners and fossil fuels.
Next, bureaucracies need to be be slimmed down and modernised. All EU countries should offer the ability to transact with their bureaucracy (tax returns, permits etc.) in the native language or English.
Finally, welfare should be ended for anyone fit and healthy below a certain age, and the retirement age taken to 70 immediately. Pensions should be phased out for anyone under 40 currently. The refugee intake should be taken to zero, and borders strictly enforced, since the net economic contribution of MENA migrants currently is negative. Access to Master's degrees should be limited to only the best students, to encourage people to enter the workforce earlier and to allow a reduction in education spending.
Through all this there could be a huge reduction in the tax burden, targeted to eliminate payroll taxes (perhaps in combination with replacing it with higher income taxes, the way Scandinavians do) and reduce VAT. Income tax/payroll tax savings could be preferentially targeted to couples with 3 or more children, to encourage higher birthrates.